STUDIES ON SEX IN CREPIDULA 9 



vesicle are not developed. The shell is often flat, thin, sym- 

 metrical and without growth marks. From what has been said 

 on shell formation it will be clear that the neuters must have 

 developed on a smooth, unrestricted surface, and this is really 

 the case; for they are most often found on 'new' hermit shells 

 with no larger individuals present. They are the first occupants. 



The writer finds that there are not only these sexually inactive 

 animals of the same sizes as males, but there are also neuiy de- 

 veloping males and males with the testis in a state of degenera- 

 tion. Evidently the gonad does not necessarily undergo male 

 development, nor the accessory male organs appear, when the 

 animal has reached any certain size. Given several specimens 

 of the same size, some may be sexually inactive; some may have 

 an immature testis developed to the spermatogonial, or sperma- 

 tocytic, or spermatid stage, as the case may be, with the sperm 

 groove and seminal vesicle forming and the penis growing out 

 behind the right tentacle; some may be mature males; some 

 may be males with the testis in any conceivable state of retro- 

 gression — one, several or all the stages of spermatogenesis lack- 

 ing — and with the penis partly atrophied. Examples of all the 

 above conditions are obtainable, in any size from 2 to 20 mm. 

 length or even outside those limits, and they may all be found 

 at many different seasons of the year. A partial analysis of this 

 phenomenon by means of experiment has been attempted in a 

 paper to follow the present one. At present it is necessary 

 only to state that the conditions occur and that the case seems 

 to be unique. 



Orton has described ('09) the sex relations in the 'chain 

 formations' (Conklin) of Crepidula fornicata. "Individuals of 

 this species associate permanently in linear series to form 

 'chains.' All lengths of chain composed of as many as 12 

 individuals have been found." Orton showed that the largest, 

 most proximal individuals in such a colony were usually females, 

 the smallest and most distal ones males, and between the two 

 were all stages from the male to the female phase including 

 hermaphrodite forms. He pointed out that the proximal ani- 

 mals were the oldest members of the colony, and had undoubt- 



