THE AMERICAN NATURALIST. [Vol. XXXVIII. 



that the eggs are fertUized and probably the sperm in the 

 annuhis is used for that purpose. But, unfortunately, the mode 

 of fertilization or even its actual occurrence has not been made 

 out. The sperm plug may remain visible for a few days after 

 laying but it then disappears. Its appearance also is changed, 

 its end broken, after laying. Examination of the contents 

 of the annulus after laying showed very few sperms. As the 

 eggs are laid they probably pass over the annulus and a relatively 

 small amount of sperm might fertilize all of them if it came out 

 of the sperm plug at the right time. Before laying the annulus 

 is covered with glair and possibly this may act to bring the 

 sperms out as well as to protect them from the water, which 

 produced marked and apparently destructive changes in the 

 sperms. Some osmotic factor may here be concerned in bring- 

 ing out the sperm. Other means of getting the sperm out from 

 the waxy tube that we have called the sperm plug and from the 

 interior of the annulus might be : the pressure that the sternal 

 plate between the fifth legs may exert upon the annulus when the 

 legs are forced forward, as sometimes seemed to be the case 

 about the time of laying ; or some activity of the small pleopods 

 of the first abdominal somite. The former action, however, 

 seems only to force the annulus to face more vertically in place 

 of horizontally while the necessity of the first pleopods as 

 instruments in fertilization was disproved by cutting them off 

 from a female about to lay and finding that the eggs under- 

 went normal cleavage as if fertilized. 



In support of the view that the sperm issue from the annulus 

 at the time of laying it was found that if the annulus was then 

 removed the female seemed not to be inconvenienced, going 

 through turning movements as usual, but the eggs did not 

 develop. This may, however, have been due to the fact that 

 the female was lifted out of the water, the glair disturbed and 

 thus both eggs, and presumably sperm, exposed to the water, 

 which may have prevented fertilization even if the sperm were 

 upon the eggs. 



No sperm were found upon the eggs nor upon the annulus : 

 when sperm are taken from the male or from the annulus 

 they undergo changes of form which might make then> less 



