148 RAYMOND BINFORD 
1. INTRODUCTION ° 
In spite of the extensive researches into the spermatogenesis 
of the Decapods, the use of the peculiar structures found in the 
spermatozoa of these animals is still an unsolved problem. This 
is due to the fact that the entrance of the spermatozoon into the 
egg has never been reported. While studying the habits and 
structure of Menippe mercenaria, a large edible crab found along 
the southern part of the Atlantic coast of the United States, I 
had the good fortune to obtain material which shows the essen- 
tial features of this process. In order to show which parts of 
the seminal cell are involved in the process of fertilization, the 
genesis of the spermatozoa and the formation of the pronucleus 
in the fertilization of the egg, as well as the entrance of the 
spermatozoon, are here described. The history of the male cell 
from its origin in the epithelium of the wall of a tubule of the 
testis to its association with the female nucleus in the center of 
the egg, is here presented. 
2. SPERMATOGENESIS 
The testis 
The testis of Menippe is a large paired organ lying just under- 
neath the dorsal wall of the carapace. The inner ends of the 
right and left portions lie close together, just anterior to the 
heart and from here diverge anteriorly and laterally to the outer 
edge of the carapace. It is composed of relatively long and 
complexly folded tubules which vary in diameter from 0.14 to 
0.33 mm. The deferent duct, one on each side, leads from the 
a 
A. Andrews, and at every step in the progress of this work I have received his 
kind advice and helpful criticism. I am also greatly indebted to the Hon. Geo. 
M. Bowers, United States Commissioner of Fish and Fisheries, for the privilege 
of working in the Marine Biological Laboratory at Beaufort, North Carolina, 
and for the liberal help extended to me in carrying on my researches there. My 
thanks are also due to Mr. H. D. Aller, Director of the Laboratory, for his ready 
cooperation in placing at my disposal the conveniences necessary for carrying 
forward my work. ’ ’ 
