NO. 2 hyman: polyclad FLATWORMS FROM THE GALAPAGOS 189 



determined. A general sagittal view of the copulatory apparatuses is 

 shown in fig. 6. The rounded prostatic vesicle forms the proximal end 

 of the male apparatus. It is covered with a thick layer of muscle fibers 

 forming its contour, and the interior is divided into radiating glandular 

 chambers of eosinophilous nature. The oval seminal vesicle lies ventral 

 to the prostatic vesicle. It has a thick muscular wall. The sperm ducts 

 could not be traced outside the seminal vesicle, but the common sperm 

 duct enters the ventral wall of the vesicle as shown in fig. 6, and pursues 

 a slanting anterior course in the muscular wall before opening into the 

 lumen. The rear end of the seminal vesicle makes an upward bend and 

 narrows to an ejaculatory duct that, after coming in contact with the 

 prostatic duct, runs alongside the latter and ventral to it. The two ducts 

 open together on a papilla projecting into the beginning of the lumen of 

 the cirrus sac. The cirrus sac is a muscular oval body, broad anteriorly 

 and gradually narrowing posteriorly. It is ensheathed in a thick mus- 

 cular coat outlining its contour and somewhat constricted from the mus- 

 cular coat of the prostatic vesicle. The anterior and larger part of the 

 cirrus sac consists of a tissue web in which muscle bands run diagonally 

 backward, converging to a penislike eminence projecting into the armed 

 part of the cirrus sac. The lumen of the anterior part of the cirrus sac 

 forms an ejaculatory duct. The part of this lumen that receives the 

 prostatic duct and duct from the seminal vesicle is wider and has thinner 

 walls than the remainder, which is a narrow tube with a definite mus- 

 cular wall. It continues backward in a sinuous manner and opens through 

 the penislike eminence just mentioned, which projects into the consider- 

 able cavity of the rear part of the cirrus sac. This cavity and the emin- 

 ence are covered with backward directed curved spines, that are slightly 

 larger toward the posterior end of the cirrus sac. This forms another 

 penislike projection housed in the male antrum, a cavity of fair size 

 exiting by the male gonopore. The spines of the cirrus sac are borne on 

 numerous folds that are underlain by a heavily staining tissue that ap- 

 pears to be cuticularized. It does not show any definite histological 

 characters. 



In addition to the many small spines lining the lumen of the cirrus 

 sac, there are three very large spines or teeth at the exit of this lumen 

 into the male antrum. These do not appear in a median sagittal section, 

 since they are located in the lateral walls of the distal end of the cirrus 

 sac. There are two large spines in one wall at the same level, and an 

 even larger one in the opposite wall, posterior to the other two and with 

 its point almost reaching the male gonopore. These teeth are borne on 



