170 
BULLETIN OP THE UNITED STATES FISH COMMISSION. 
Peculiar concretions are developed in tlie intestine of the embryo when 5 or 6 
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 1843 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 stainable, apparently structureless core, surrounded by a nonstainable 
substance. The latter has distinct concentric strim and resembles the cyst of a para- 
site. A concretion teased from the intestine of a similar embryo is illustrated in 
figure 256. 
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. 
