285 



7) At a definite stage in the process the male always passes either 

 the right or the left fifth, or last, walking leg across under his thorax 

 so that it projects horizontally from the other side. This limb then 

 holds the first and second male pleopods, the intromittent apparatus, 

 depressed at an angle of more than forty-five degrees from the ven- 

 tral surface of the male and thus ensures their entrance into the annu- 

 lus when the male moves forward over the female. 



8) During the process the ventral sides of the two animals are 

 closely applied to one another and the abdomen of the male partly 

 encloses the abdomen of the female. The latter lies in the back or 

 partly on one side and is firmly held by both large chelae of the male 

 which grasp all the chelate appendages of the female. 



9) There is no wide distribution of sperm as has been described 

 for Astacus : it is all placed in the annulus. The oviducts of the fe- 

 male are not concerned in the process of conjugation. 



Since the sperm rapidly disintegrates when removed from the 

 protecting secretion that envelops it in spermatophore like masses and 

 the male organs in this species are so nicely adjusted to convey it to 

 the annulus, we may assume that the different forms the annulus pre- 

 sents in difi'erent species may be correlated with the well known 

 differences in the male organs so that in all the sperm is placed in a 

 protected cavity by tools that will not operate in other species thereby 

 tending to maintain specific distinctness. 



During the process of conjugation the small pleopods of the first 

 abdominal segment of the female lie with their tips near the annulus 

 and the male intramittent organs. As they tend to disappear or are 

 quite lost in Astacus, Avhere no such carefully adjusted process of 

 sperm-transfer takes place, we may suppose that in Gambarus they 

 function as sense organs to assist in the more accurate adjustment of 

 the male and female organs. 



In the one case in which eggs were laid in captivity the nervous 

 system of the female was very irritable for several days. During this 

 time by assiduous labour with both of the fifth walking legs she care- 

 fully removed all foreign matter from the ventral surface of the ab- 

 domen and from the pleopods. 



The sperm plug remained in the annulus for two days after the 

 eggs were laid and then disappeared. It was probably removed by the 

 female. The process was, however, abnormal and the eggs did not 

 develop. 



Johns Hopkins University , Baltimore Md., U.S.A. 



