a. The appendages; paired differentiations of the blastodermal area, separated by a median space (more or fewer will be seen).

B. The labrum; an oval median outgrowth, situated about on a level with the first pair of appendages. y. The abdominal papilla; now elongating.

If the specimen be a young one the involution to form the mouth may be seen immediately behind the labrum; that to form the anus, under cover of the abdominal papilla. If it be an advanced one, segmentation of the papilla will be very distinct.

8. The optic pits; two small round differentiations within the procephalic lobes (c. a.).

. The carapace; now appearing as a marginal thickening of the blastoderm, immediately external to the appendages. It is at first paired, the two folds meeting behind the abdominal papilla.

e. The hatched embryos. To be found in numbers, fixed to the swimmerets of the mother.

a.

In general they resemble broadly the parent organism. Examine—

The cephalo-thorax; more arched than that of the adult, owing to distension by the food-yolk, not yet completely absorbed. The rostrum is bent downwards and the cervical groove is, at best, ill defined.

B. The cephalo-thoracic appendages; differing but little from those of the adult. Remove and examine the free-end of the chela; its pincers

e.

apparatus is spinous and recurved at the tips, for purposes of attachment to the parent.

y. The abdomen; fully segmented and terminating in the telson. Four pairs of appendages are alone free, the first and last pairs being buried beneath the larval integument.

Look for and examine stages intermediate between c and d.

f. The larval Lobster, when about half an inch in length. Obtain if possible a specimen in which the abdominal appendages are first appearing. Compare generally with the Crayfish larva and note especially—

a. The exoskeleton; like that of the Crayfish larva, a continuous uncalcified cuticle.

B. The carapace; terminating in front in the rostrum, which assumes the form of an immense protective spine.

y. The abdomen; fully segmented and bearing several γ. smaller protective spines.

8. The eye; its great size at this stage.

e. The antennary organs; both are short and completely under protection of the rostrum.

. The thoracic appendages. The third maxillipede, great chela and ambulatory appendages, are more nearly uniform in size than in the adult; they all bear well developed exopodites.

g. Remove the second ambulatory appendage and the swimmeret of the third abdominal somite. Examine them side by side, and note in both

a. The great relative size of the protopodite.

B. The increase in length of the endopodite over the exopodite; little marked but obvious in the case of the abdominal appendage. (Cf. the corresponding abdominal appendage of the adult Crayfish.)

III.

THE EARTHWORM (Lumbricus terrestris).

THE Earthworm is to be found wherever damp earth is accessible, no matter how hard or stony the surface; the presence of moisture is indispensable to its existence. Into this earth it burrows, excavating a tubular habitation to which it repairs during the day time, emerging at night to seek food and to work, or at early morning to reproduce its species. It remains within the burrow throughout both the winter and the dry summer seasons.

The interior of the burrow is smooth and frequently lined with minute stones; its mouth is often surrounded with "castings" and plugged with leaves drawn in by the animal itself, or covered, as with a lid, by stones sometimes of relatively great weight and size.

The body of the worm is fairly uniform in dimensions throughout; it is bilaterally symmetrical, both mouth and anus being situated at opposite ends. The metameric symmetry such as was seen in the abdomen of the Crayfish, is here common to the whole body, which can no longer be subdivided into well-marked regions. It is constricted externally into a number of repetitional segments or somites, of which there may be, in a sexually mature animal, as few as 68 or considerably more than 200. For each of these somites there is a similar repetitional series of certain of the internal organs. Each somite is subdivided externally into

at least two lesser divisions or zonites, these however are but skin deep and in no way correlated with the internal parts. The body is invested in a continuous uncalcified exoskeleton in the form of a delicate iridescent cuticle. No limbs of any sort are present, and locomotion is effected by means of four longitudinal series of bristle-like seta, which project freely from all but some few of the anterior segments; a powerful muscular apparatus is developed in connection with each of these, and the chitinous setæ themselves are largely buried in tegumental sacs lined by cuticular involutions. The setæ are replaced when cast off.

The posterior terminal segments of the body are, during life, flattened from above downwards, and when the animal on removal from its burrow is observed crawling, a characteristic spatulate appearance is imparted to that region, at the upturned end of which the anus is situated. Under ordinary circumstances the worm, on coming to the surface, retains its hold on its burrow by means of this expanded extremity.

The Earthworm is omnivorous, living mainly upon leaves (for certain kinds of which it has a decided preference), and less conspicuously upon both animal and vegetable organisms ingested with the earth passed through its alimentary canal, in burrowing or otherwise. The alimentary canal is a straight tube, running the entire length of the body. The mouth leads into a thin-walled eversible buccal sac, which opens into a spacious muscular suctorial pharynx; this, in turn, passes into a long tubular oesophagus, the terminal fifth of which is enlarged to form a distensible crop. The crop is, in the common earthworm, succeeded by a whitish thick-walled gizzard, so called as it performs a mechanical crushing action. This finally opens into a long sacculated intestine, which is continued on with but slight modification.