1 76 J. THOMAS PATTERSON. 



An interesting periodicity in the reproduction of G. gemellipara 

 occurs at Woods Hole. From the 2oth to the 25th of June (191 1), 

 shortly after the writer arrived there, specimens were secured 

 in considerable numbers, but from this date until about the loth 

 of August it was extremely difficult to obtain material, although 

 molluscs from many different regions were examined. From an 

 entire bucketful of the Modiolus not more than a dozen would 

 be secured, and these were either very young, sexually immature 

 animals, or very large individuals which were about on the point 

 of undergoing degeneration and freeing their young. About the 

 middle of August, both in 1910 and 1911, Graffillce were secured 

 without difficulty, but from the 25th of the month until the I2th 

 of September, when I left Woods Hole, they were extremely 

 scarce. From this it would seem that there are two summer 

 periods of rapid multiplication, one in June and the other in 

 August; and possibly a third period occurs in October. Linton 

 reports that Coe found Graffilla in abundance at New Haven 

 during the month of October. 



At no time does one find G. gemellipara in such numbers as 

 reported by some of the writers on the other species of the genus. 

 Jameson, '97, states that from four to several dozen individuals 

 of G. buccinicola, which is parasitic in the kidneys of Bnccinum 

 undatiim and Fusus antiquus, are found in every specimen of the 

 two molluscs. 



II. STRUCTURE OF THE REPRODUCTIVE ORGANS. 



The reproductive organs of this Graffilla arc difficult to make 

 out, both on account of the viviparous method of reproduction as 

 well as on account of the variability in the development of the 

 different parts. G. gemellipara, like certain other members of 

 the genus, exhibits successive hermaphroditism, but the case is 

 not so extreme as that described for G. buccinicola by Jameson, 

 '97. The male organs develop first and upon reaching their 

 maturity at a comparatively early period in the post-natal life, 

 in part atrophy, and are then followed by the development of 

 the female organs. 



The male organs consist of the following parts: (i) a pair of 

 testes which lie just posterior to the pharynx, one- on each side 



