SPERMATOGENESIS OF AMERICAN CRAYFISH 599 



arms adhere to the ovum. Then the explosion of the capsule 

 occurs, thus tending to drive the nucleus through the chorion 

 into the egg. Koltzoff observed only a single case of such fertili- 

 zation. 



Spitschakoff ('09) worked on the spermatozoa of the Caridea, 

 mainly on the species Leander adspersus Rath., and L. squilla. 

 He goes fully into the transformations undergone by the sper- 

 matid to form the spermatozoon and finds that they are similar 

 in many respects to those of other decapods. Spitschakoff 

 also studied the fertilization process in these forms and believes, 

 with Koltzoff, that, during fertilization, the nucleus of the sperm 

 is driven through the chorion of the egg by means of the changes 

 undergone in the vescicle of the spermatozoon. 



Retzius ('09), worked on the spermatozoa of Palaemon squilla, 

 Crangon \ailgaris, Hippolyte, Nephrops norvegicus, Homarus 

 vulgaris, Astacus fluviatilis, Calocaris macandrae, Eupagurus 

 bernhardus, Galathea squamifera, Porcellana longicornis, Litho- 

 des maja, Stenorhynchus rostratus, Hyas coarctatus, H. araneus, 

 Eurynome aspera, Portunus depurator, P. pusillus, Ebalia 

 tumefacta, Carcinus maenas and Cancer pagurus. 



In general, the structure of the sperm of these forms is about 

 the same, and its genesis is similar to that described by Grobben, 

 Gilson, and Koltzoff. The head piece is derived from the nucleus 

 and it may be round, hemispherical, lens-shaped, or of another 

 form. The vesicle, the so-called 'Schwanzkapsel' of the German 

 investigators, assumes various forms, being rod-like, needle- 

 like, spiral-like, cone-like, spherical, hemispherical or lens-like 

 in its shape. Within this vesicle an axial tube is always dis- 

 cerned, and this contains numerous structures, among which is 

 the central body. Also a nebenkern organ is often found which 

 sometimes produces the radial arms, and may assume other forms. 



Binford ('13) described the male germ cells and the process of 

 fertilization in the sea-crab Menippe mercenaria. He briefly 

 touches on the maturation divisions, but describes the trans- 

 formations of the spermatozoon rather fully. 



In the testis a single row of cells persists along one side of the 

 tubule and these give rise successively to batches of spermatozoa. 



