ONTOGENY OF THE ANNULUS VENTRALIS. 



E. A. ANDREWS. 



Ill crayfish of the genus Cambarns there is a sperm receptacle 

 in the female which has been known as the Annuhts ventralis 

 and made use of as a specific character in systematic works. 



Nothing has been known of its mode of development beyond 

 the brief mention by Mary Steele L who figured the external views 

 of the annulus in specimens of C. gracilis, 20, 22, 27.5, 30, 35, 

 36, 50 and 60 mm. in length. Of these the latter four were 

 probably adults and the former four immature young. These 

 figures show an increasing complexity of external sculpturing 

 and an increase in relative longitudinal diameter ; however, as 

 they were made incidentally and without reference to the use or 

 internal structure of the organ they are necessarily insufficient. 

 While the annulus is a necessary reproductive organ in Cam- 



KlG. I. 



barus it is also a new organ in the history of crayfish since it is 

 found only in the most specialized form, Cambarns. It seemed, 

 therefore, of interest to find out just how and when the organ 

 develops in the ontogeny of Cambarns. 



The following account of the origin and growth of the annulus 

 refers almost exclusively to Cambarns affinis reared in the labo- 



l (J>iii'. of Cin. Bulletin, X., 1902. 



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