170 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Peculiar concretions are developed in the intestine of the embryo when 5 or (5 

 weeks old, as shown in figure 233, plate 51, and persist up to the time of hatching 

 (fig. 30, pi. 18). They were noticed as early as 1813 by Erdl (62). We see them to 

 better advantage in a section of the intestine of a much older embryo, as in figure 

 253, P. There is great variation in both the size and shape of these bodies, but they 

 consist of a staiuable, apparently structureless core, surrounded by a nonstainable 

 substauce. The latter has distinct concentric stria? and resembles the cyst of a para- 

 site. A concretion teased from the intestine of a similar embryo is illustrated in 

 figure 250. 



In the living animal they have a white lustrous appearance, and are quite conspic- 

 uous, moving to and fro with the peristaltic contractions of the intestine. On the 

 suspicion that they might be of a parasitic origin I submitted them to Dr. Stiles of the 

 United States Bureau of Animal Industry. He has kindly examined them, and con- 

 cludes, so far as it was possible to reach a conclusion from the material at command, 

 that the bodies in question were nonparasitic. In this event it is probable that they 

 are the faecal residue of the egg yolk which undergoes digestion in the course of 

 embryonic life. The animal is entirely rid of them soon after hatching. 



THE HATCHING OF THE LARVA. 



A lobster in the act of hatching is represented in fig. 29, plate 18, and one teased 

 from the egg in fig. 30. The embryo at this time is inclosed by three membranes, 

 namely: (1) the outer or secondary egg membrane; (2) the primary egg membrane, 

 improperly called the chorion ; (3) a larval membrane, which is seen inclosing, like 

 a glove, the various appendages in fig. 30. These are better shown in a much distended 

 condition in cut 20, plate F. In this case, however, the innermost cuticle is not the 

 larval membrane, but an earlier embryonic molt, which is absorbed long before the 

 time of hatching is reached. 



When burst by internal pressure the secondary egg membrane splits (in the ver- 

 tical longitudinal plane of the embryo) into two halves like the cotyledons of a beau, 

 and is drawn off in most cases over the head by the strand or stalk with which it is 

 continuous. It is a thick, translucent bag of a yellowish-brown tint, slightly elastic 

 and easily torn. It completely separates from the underlying membrane, except at 

 one point, that beneath the stalk of attachment. Here it adheres to the primary 

 membrane, which has now become reduced by distention into an exceedingly delicate 

 pellicle. In this particular case (fig. 29) it was whole, until ruptured by needles (just 

 above eyes), and thus completely inclosed the exposed parts of the embryo. When 

 the outer membrane of attachment bursts, it contracts and usually drags the delicate 

 inner cuticle away with it. The embryo thus slips out in the condition shown in 

 fig. 30. 



This is a very critical period in the life of the artificially hatched lobster. If it is 

 healthy it soon molts, the swimming hairs are rapidly evaginated, and it emerges into 

 what may be properly called the first locomotor larval stage. If less fortunate, it lies 

 on its back for hours, struggling to get clear of some part of its larval covering. The 

 failure to pass this molt is the cause of death to many embryos which have been reared 

 successfully up to this point in the hatching jar. 



