POLYCLAD FLATWORMS — HYMAN 589 



band of small eyos, not definitel}^ divided at the middle, numbering 

 about 35 in the 4-mm. specimen (fig. 166), about 40 in the 5-mm. 

 specimen (fig. 16c). The cerebral eyes are large and relatively few in 

 number, ranging from 8 to 12 on each side, in the two specimens. A 

 marked feature of the eye pattern is the presence of a single isolated 

 eye on each side at the level of the anterior end of the cerebral groups. 

 Such a pair of eyes set apart from the cerebral gi-oups is known in a 

 number of species of Prosihiostomum and therefore is not diagnostic. 

 Some authors speak of this pair of eyes as ventral but in my material 

 the pair appears on the same level as the other cerebral eyes. The 

 large tubular pharynx, often partly protruded or discarded on fixation, 

 has remained in situ in the smaller specimen but was missing from the 

 larger one There appeared to be no median intestinal branch above 

 the pharynx. Beneath the posterior end of the pharynx is seen the 

 terminal part of the male apparatus, at the attached end of the pharynx 

 is located the female gonopore, and shortly behind the latter occurs the 

 sucker. 



CopxjLATORY apparatus: Both specimens are sexually mature. 

 The larger specimen was sectioned sagittally, and a sagittal view of the 

 copulatory structures is shown in figure 17a. The male and female 

 gonopores and the sucker lie close together but the distance between 

 the two gonopores is slightly greater than the distance between the 

 female gonopore and the sucker. The male gonopore leads into a 

 long tubular antrum, slanted forward so as to lie almost parallel to 

 the ventral body wall. At the anterior end of the male antrum is 

 seen the penis, an oval body containing the usual penis stylet, whose 

 tip is protected by the penis sheath projecting into the antrum as a 

 slight elevation. Details of the penis were not very clear in the sec- 

 tions; the usual eosinophilous granulation, indicative of prostatic 

 secretion, appeared present in the wall around the stylet. The proxi- 

 mal end of the penis receives the ejaculator}^ duct and the ducts of 

 the two accessory vesicles. The latter are the usual round muscular 

 bodies with small lumen and thick wall of circular fibers. They occur 

 one behind the other. The more posterior one lies just behind the 

 level of the proximal end of the seminal vesicle; tiie other is located 

 on the other side of the seminal vesicle at a level just below the poste- 

 rior end of the latter. The seminal vesicle is retort-shaped, curved on 

 itself; its proximal end is rounded with a thick wall of muscle fibere 

 paralleling its contours ;distally, as the vesicle curves posteriorly parallel 

 to itself, the muscular wall thins. The entrance of the sperm ducts 

 into the seminal vesicle could not be followed. The spermiducal 

 vesicles swollen with sperm are obvious alongside the seminal vesicle. 

 They have been omitted from figure 17a to avoid complicating it. 

 One occurs above the seminal vesicle and the other below, but the usual 



