NATURAL HISTORY OF AMERICAN LOBSTER. 
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decapod crustacean but comparable to the flagellate spermatozoa of other animals. 
The crustacean sperm becomes differentiated in three parts, namely, (1) the nucleus or 
head, (2) mitochondral body (a partly fibrous and partly granular structure) repre- 
senting the neck or middle piece, and (3) the explosive capsule or modified tail. 
The sperm cell develops processes (fig. 31,1) which in the lobster arise from the neck. 
They ordinarily appear to be immobile and are distinctive of the decapod sperm. The 
number of these processes varies from 1 to 10, but 3 is a common number, which is 
found in Homarus, Palinurus, and Galathea, as well as in some of the crabs. The 
number is of physiological importance, since they are used for orienting the sperm upon 
the egg in fertilization. In the true crabs the processes arise from the head and are 
therefore nuclear in origin. It may be added that in the prawns (Candida) the usual 
processes are lacking, but the capsule ends in a sharp thread-like tail. In the crayfish 
(. Astacus ) and many crabs, as well as in Gebia and Callianassa, the neck and capsule 
are reduced in size and pressed against the head. 
The processes are supported by a central mitochondral, skeletal fiber, or bundle of 
fibers. If in the course of development of the spermatid, 
these strong skeletal fibers project from the cell body with 
free ends, appearing to draw after them the more fluid 
constituents of the cell. The skeletal fibers can be demon- 
strated by plasmolyzing the cell or surrounding it with a 
solution of higher osmotic pressure. These skeletal fibers 
are really bundles of fibrils, which have a tendency to spiral 
winding. 
The capsule (fig. 31, 1 and 2) is a double walled cylin- 
drical body, a median tube running through it from end 
to end. This tube is formed by a median invagination ex- 
tending from the hinder end forward to the neck, and is 
expanded at either extremity into a widechamber. The 
distal opening is closed by a plug of chitin. A peculiar rod 
or “Polster” of stainable substance is pressed from the central body into the anterior 
chamber. In the ripe sperm the outer capsular wall and the axial tube consist of 
chitin, and may be regarded as continuous, except at the point pierced by the “ Polster.” 
This stainable rod is often constricted into a proximal central body in the neck and a 
distal central body in the capsule (p and deb). 
FERTILIZATION. 
In the lobster the sperm cells pass a long latent or resting period in the sperm 
receptacle, and may retain their vitality for from one to two years, and possibly longer. 
When the eggs are laid, the sperms leave their receptacle, find the eggs, and fertilize them. 
The spermatazoa are either pressed out by mechanical force, or else they must be 
aroused to activity by a definite stimulus, probably of a chemical nature. 
Fig. 32. — Diagrammatic section of 
sperm cell in capsular explosion, as 
seen in plane a a, figure 31 (3); fd. 
in . t . , folded inner tube. 
