328 BULLETIN OF THE BUREAU OF FISHERIES. 



which the eggs are attached to each other and to the body of the mother, in consequence 

 of internal pressure, splits lengthwise of the embryo and its two halves separate like the 

 skin of a pea. The primary eggshell or transparent "chorion," reduced by distention to 

 a sac of great tenuity, adheres to the outer capsule at a point usually beneath its stalk 

 and is in turn apparently adherent in some degree to the embryonic cuticle. Further, 

 the invaginated hairs or setae of the larva about to issue stick by their tips to the cuticular 

 sheaths of the corresponding setas. Consequently, successful hatching in the lobster 

 means shedding the egg membranes with the old cuticle and the pulling out of the 

 invaginated hairs of the new chitinous covering at the same time. Hatching and mol(»- 

 ing thus go hand in hand, and the first larval stage, like every period which follows, is- 

 preceded by a molt. The fact that hundreds of the larvae which are hatched by artificial 

 means get clear of the eggshells, but die through inability to cast this embryonic cuticle, 

 illustrates the importance of these nicely adjusted relations. 



It is thus evident that we can not help the little lobster out of its shell, but must let 

 it escape in its own way, and if healthy it will cast in a few minutes. Its old covering 

 must be shed in one piece and with the loss of as little energy as possible. The infant 

 lobster hatches, molts, and unsheaths its swimming hairs at the same time," as was 

 explained more fully in an earlier chapter (see ch. vi, p. 236). The eggshell, as we have 

 also seen, sticks both to mother and child, while the cuticle of the latter is in turn glued 

 to the swimming hairs of the new skin, so that every tug at the shell helps to free the 

 little lobster from its hampering cloak and at the same time to perfect its swimming 

 apparatus. 



The young lobster is very compactly folded in the egg, which becomes ovoidal in 

 consequence of growth. At the time of hatching this marked ovoidal form of the 

 embryo is largely determined by the form of the carapace, which is longer than broad. 

 The body is bent, but not twisted, the tail, as in all crustaceans, being folded against 

 the thorax and head, the tips of the telson plate even reaching beyond the compound 

 eyes and to a point overlying the masticating stomach. The mouth is thus covered by 

 the overlap of the hinder part of the fifth somite of the abdomen, which also presses 

 against the downwardly bent rostrum and the mouth parts. The antennae are directed 

 backward along the free borders of the carapace, while the thoracic appendages with 

 their outer branches, like a double bank of oars, are directed downward over the abdo- 

 men and forward toward the middle line. Hatching thus implies not only release from 

 the egg membranes, but casting off a complete cuticular molt and at the same time 

 the evaginating or drawing out of every telescoped hair and spine of the body, including 

 the rostrum; further, in addition to this and aided by it, the unfolding of the abdomen 

 and the straightening of the telson and the various appendages. 



I^ittle difference in the size of the eggs was noted by Anderton (5) in the European 

 lobster until the last month of development, when they increased as much as 3 milli- 

 meters in length in conformity to the shape of the embryo, and when convulsive move- 

 ments of the embryo itself were often violent enough to move the egg from under the 

 object glass. 



