17 



agree as to which part of the cell is the nucleus. They like- 

 wise desorihe a vesicle which arises in the cytoplasm either 

 against the nucleus or close to it, and mention the substance 

 of cytoplasmic origin which appears hetween the nucleus and 

 the vesicle. Most of them see a structure like the central 

 body and describe the inner tubule. There are many variations 

 in the detail of the development of these last two structures 

 and different species seem to differ widely in this respect. 

 There is mxxch disagreement concerning the destiny of the nu- 

 cleus and the origin and nature of the substance in the cap- 

 sule. These points of disagreement do not however affect the 

 statements I have made concerning the structure of the mature 

 sperm. It is with this structure that we have to do in the 

 further course of the present investigation. 



III. Copulation . 



We come now to the question of the transfer of the sperm- 

 atophores from the body of the male to that of the female, 

 from the deferent duct to the seminal receptacle. We there- 

 fore turn our attention from the sperm itself to some of the 

 habits of these crabs. Menippe mercenaria lives in crevices 

 under or between the rocks or in burrows which it digs in 

 the mud along the shore a little below low water line. Usual- 

 ly one crab is found in each burrow, but occasionally, and 

 even frequently in the month of August, a male crab will be 

 found guarding a hole in which there is a female. Sometimes 

 the female thus found has a soft shell. If its shell is 



