TYPE PLATTHELMINTHES. 



139 



in the Triclads otocysts are wanting, uor have ciliated lateral 

 depressions been described as occurring in the order. 



Little is known concerning the 

 excretory system. The reproduc- 

 tive system differs from that of 

 the other orders in that the male 

 and the female apparatus each 

 possess a separate opening ( 3 and 

 ? ), there being no genital atrium 

 common to both. Both apertures 

 lie behind the mouth-opening, near 

 the posterior end of the body, 

 the male apparatus opening an- 

 teriorly to the female. The former 

 is similar in structure to what has 

 been described for the Triclads. 

 The female apparatus possesses 

 no vitellarium, and the ovaries {ov) 

 are very numerous, lying in the 

 lateral parts of the body, their 

 various ducts uniting to form wide 

 canals which serve as uteri {ut). 

 These open into a single tube, the 

 vagina, which receives the secretion 

 of the numerous glands {sg) which 

 form the shell-gland. 



In some forms there is situated 

 about the middle of the ventral 

 surface of the body a muscular 

 sucker which serves as an organ of 

 adhesion. Since the presence or 

 absence of this organ is in either 

 case associated with the occurrence 

 of other important structural pecu- 

 liarities, the order has been divided 

 into tw6 suborders — the Ootylea, 

 provided with a sucker (Thysano- 

 zoon, Eurylepta), and the 

 {Planocera, Leptoplana). 



Fig. 74.— a Poltclad Tukbbl- 

 LAKIAN, Leptoplana alcindi 

 (after Lang). 



ag = accessory gland. 



ce = cerebral ganglion. 



oi> = ovary. 

 p7i = pharynx. 



sg = shell-gland. 



ie = testis. 



ut = uterus. 



i>d = vas deferens. 



vs = vesicula seminalis. 

 ^ , 2 = male and female orifices. 



Acotylea, in which it is absent 



