STUDIES ON SEX IN CREPIDULA 45 



cal. In C. plana there is no indication that they point to any 

 abnormal condition, and it is more likely that they have some- 

 thing to do with the passage of the egg through the oviduct. 



b. The uterus and seminal receptacles. The development of 

 the uterus has not been taken up in detail. In its more general 

 features it agrees with the account given by Giese ('15) for 

 Catyptraea and Crepidula unguiformis, viz., it arises by a deep- 

 ening and closing of the proximal part of the sperm groove at 

 the opening of the goniduct near the shell muscle. Subsequently 

 it extends both backward and forward from that point and its 

 walls become transformed into a very high columnar epithelium 

 with different kinds of glandular elements. Giese states that 

 there are no cilia in the uterus of C. unguiformis. In C. plana 

 the inner wall of the uterus is uniformly ciliated in all parts of 

 the organ. In C. miguiformis the seminal receptacles are de- 

 scribed as consisting of thi'ee pouches arising as evaginations of 

 the uterus and opening separately into it near the oviduct. They 

 are flask-shaped and not ciliated. In C. plana the seminal re- 

 ceptacles likewise arise as evaginations from the uterus; but there 

 are at least nine of them, each with its own opening into the 

 uterus, the openings being very close together. Each receptacle 

 is composed of a thin-walled, non-ciliated sac connected to the 

 uterus by a narrow tube whose wall is a cubical, ciliated 

 epithelium. 



c. The gonopericardial duct. No mention has been made 

 thus far of the gonopericardial duct in Crepidula plana. This 

 structure was discovered by Giese in Calyptraea and in Crepi- 

 dula unguiformis, but found to be lacking in Capulus. 



In Crepidula plana the gonopericardial duct is present. It 

 arises, as in the two forms above mentioned, from a strand of 

 mesenchyme cells which connects the most anterior extension of 

 the pericardial chamber with the middle of the oviduct. It is 

 never seen during the male phase regardless of the size of the 

 animal, but becomes evident before the assumption of the fe- 

 male phase, during the period when the oocytes first reach the 

 synaptic stages. The originally solid strand becomes hollow, 

 and during the early growth period of the oocytes it begins to 



