body. Soon this sac-like body grows longer, and contracts at intervals; the intervening parts become unequally enlarged, some segments or rings, formed by the contraction of the body-walls, greatly exceeding in size those next to them; and it thus assumes the appearance of a being, more or less equally ringed, such as in the young Terebella, here figured, where the cilia are restricted to a single ring surrounding the body. Gradually the cilia disappear and regular locomotive organs, consisting of minute paddles, grow out from the side; feelers (antennæ), jaws, and eyes (simple rudimentary eyes) appear on the few front rings of the body, which are grouped by themselves into a sort of head, though it is difficult in a large proportion of the lower worms, for unskilled observers to distinguish the head from the tail. In the embryo of the Crustacean, such as the Fresh-water Crawfish, as shown by the German naturalist Rathke; and also in the earliest stages of the Insect, the body at once assumes a worm-like form, thus beginning its embryonic life from the goal reached by the adult worm.

Thus we see throughout the growth of the worm, no attempt at subdividing the body into regions, each endowed with its peculiar functions; but only a more perfect system of rings, each relatively very equally developed, but all becoming respectively more complicated. For example, in the fresh-water Nais, each ring is plainly distinguished into an upper and under side, and in addition to these a well marked side-area, to which, as in the marine worm, Nereis, oar and paddle-like organs are attached; in most other worms eye-spots appear on the front rings, and slender tentacles grow out, and a pair of nerve-knots (ganglia) are apportioned to each ring.

Thus, in the Worm the vital force is very equally distrib

uted to each zoölogical element, or ring of the body; no single part of the body is much honored above the rest, so as to subordinate and hold the other parts in subservience to its peculiar and higher ends in the animal economy.

a Fig. 3.

But when we rise in the scale of articulate life, we see at once the action of a new principle. First in the Crustacean appears a broad distinction between the front and posterior end of the body. The rings are now grouped into two regions, and the hinder division is subordinate in its structure and uses to the forward portion of the body. Hence the nervous power is transferred in some degree towards the head. The organs performing the

Pandalus annulicornis Leach. A Shrimp.

a. cephalothorax; b. abdomen.

functions that distinguish animals from plants, such as locomotion and sensation, all reside in the front region; while the vegetative functions, or those concerned in the reproduction and nourishment of the animal produced, are mostly carried on in the hinder region of the body (the abdomen).

The Crustacean cannot be said to have a true head, in distinction from a thorax bearing the organs of locomotion, but rather a group of rings, to which are appended the organs of sensation and locomotion.

Sometimes the jaws become remarkably like claws; or the legs resemble jaws at the base, but towards their tips. become claw-like; gill-like bodies are sometimes attached to the foot-jaws, and thus, as stated by Prof. J. D. Dana, in the introduction to his great work on the Crustacea of the United States Exploring Expedition, the typical Crus

tacea do not have a distinct head, but rather a "headthorax" (cephalo-thorax).

When we rise a third and last step into the world of Insect forms, we see a completion and final development of the articulate plan which has been but obscurely hinted at in the two lowest classes, the Worms and Crustacea. Here we first meet with a true head, separate in its structure and functions from the thorax, which, in its turn, is clearly distinguishable from the third region of the body, the abdomen, or hind-body. These three regions, as seen in the wasp, are each provided with three distinct sets of organs, each having distinct functions, though all are governed

Fig. 4.

by, and minister to the brain force, now in Philanthus ventilabris a great measure gathered up from the posFabr. A Wood-wasp. terior rings of the body, and in a more concentrated form (the brain), lodged in the head.

From SAY.

Here, then, is a centralization of parts headwards; they are brought as if towards a focus, and that focus the head, which is the meaning of the term "cephalization," proposed by Professor Dana.* Ring distinctions have given away to regional distinctions. The former characterize the Worm, the latter, the Insect. In other words, the division of the body into three parts, or regions, is in the insect, on the whole, better marked than the division of any one. of those parts, except the abdomen, into rings. This is

In two papers on the Classification of Animals, published in the American Journal of Science and Arts, Second Series, vol. xxxv, p. 65, vol. xxxvi, July 1863, and also in his earlier paper on Crustaceans, "the principle of cephalization is shown to be exhibited among animals in the following ways:

1. By a transfer of members from the locomotive to the cephalic series.

2. By the anterior of the locomotive organs participating to some extent in cephalic functions.

3. By increased abbreviation, concentration, compactness, and perfection of structure, in the parts and organs of the anterior portion of the body.

4. By increased abbreviation, condensation, and perfection of structure in the posterior, or gastric and caudal portion of the body.

5. By an upward rise in the cephalic end of the nervous system. This rise reaches its extreme limit in Man."

well illustrated in the thorax of the Wasp. In reality the thorax of this insect consists of three rings, with a supernumary one-the first and basal ring of the abdomen— thus forming a compact mass, consisting of four of these rings. But all are so intimately united into an almost spherical, rounded mass, which is due to the unequal size of the parts composing the rings, some being enlarged, and others either diminished in size, or wholly wanting, that it needs the sagacity of a Latreille, or an Audouin, those fathers of Entomology, to detect the actual number of the elemental rings.

Appended to the head, as the legs to the thorax, are special organs of sight and touch, into which the brain is immediately projected; as the simple and compound eyes, and the antennæ, each with their separate pair of nerves. These are placed in front of the mouth. Behind the mouth, and on each side, are the jaws or mandibles, the maxilla with their palpi (or touchers), and last of all, and next to the thorax, the labium, or under lip, and its palpi. Before the larva leaves the egg, these four pair of appendages are much alike in form, budding out as simple tubercles, and their relative position and succession are as given above; but during growth they change their position, crowd forward about the mouth-opening, so as to lose nearly all traces of their normal succession, and, in consequence, the labial palpi seem to be more properly placed in advance of the maxilla, while the mandibles appear, on their part, to be inserted at the base of the head next to the thorax; and it is only by tracing their origin and development, as given in the works of Claparède and Weismann, which we shall farther notice in this journal, that we have been able to understand their normal posi

Insects, as a whole, are much smaller than the Crustacea; for example, compare a Honey bee or Hawk moth with a Lobster or Crab. This diminution of size is due to the greater concentration of parts, and their compression into a much less bulk. Crustacea are mostly inhabitants of the water, while Insects are, in some form, almost exclusively terrestrial. As the Whale exceeds in size the Dog or Lion, or Man himself, so does the Lobster surpass in bulk the Bee, though the latter is a much more highly organized animal, with a more complicated outer crust, a more complex system of nerves, bloodvessels and muscles.

There are various grades of superiority among insects. Rank among men is determined by one's superior intelligence, and less and less likeness to the savage. Thus writers on Ethnology place the European and Australasian at two extremes. On this principle the zoologist classifies animals by their greater or less resemblance to the lowest types. Thus among Articulates, the Worms are the simplest in form, and in all respects the lowest. The Crustacea are placed next in the natural system, which leaves the Insects topping the series. In classifying the subdivisions of the class of Insects, we observe the same principle. In locating an Insect in what seems to us its true place within its own group, we must follow this rule, i.e., its greater or less resemblance to the typical wormlike form, for the more the body is developed headwards the higher is its rank. Among the lowest Insects are the May-flies (Ephemera), the Panorpa, or Forceps-tail, and the Spring-tails (Podura and Lepisma). In these forms the body is slender and wormlike, and the head is many times smaller than the rest of the body. In the Honey bee however, which is the highest among all articulates, the head is but little smaller, and yet very distinct from