TYPE PLATYHULMINTUES. 



137 



VI 



ov 



ex 



The nervous system consists of a bilobed brain lying in 

 the anterior part of the body and 

 from which two nerve-cords pass 

 backwards, united at intervals by 

 cross-commissures and giving off 

 on their outer sides branches 

 which anastomose with one an- 

 other, forming a network. 



In Griinda seyintittata the transverse 

 commissures agree in number and ar- 

 rangement with the lateral branches on 

 the one hand and with the diverticula of 

 the intestine on the other, the arrange- 

 ment of the two systems producing an 

 appearance of metamerization which is 

 most striking, especially as it affects as 

 well the excretory and reproductive sys- 

 tems. In this form an indication is 

 afforded of the manner in which the 

 more pronounced and typical metameri- 

 zation of the higher types has been pro- 

 duced by the more or less completed 

 multiplication of the organs and the 

 integration of the parts so formed into 

 a metamere (see p. 43). 



Eyes are usually present, fre- 

 quently provided with lenses, and, 

 though usually two in number, 

 may be very numerous and situ- FIG. 73. A TRICLAB TURBEI.LARI- 

 ate'd along the margin of the body. AN ' Sync^lidium peUucidum (after 



No otocysts occur, and the sides 

 of the anterior end of the body 

 are in some forms produced into 

 more or less elongated processes 

 which may possibly be mainly 

 sensory in function, while behind 

 them are areas of strongly ciliated 

 cells richly supplied with nerves 

 and presumably corresponding 

 with the ciliated depressions oc- 

 curring in the same region in the Alloiocoela and Ehabdocoela. 



WHEELER). 



ex = excretory system. 

 g = accessory glaud. 

 ggl = vaginal glands. 

 n = nervous system, 

 od = oviduct. 

 ov = ovary. 



p = reproductive orifice. 

 ph =- pharynx. 

 t = testis. 

 u = uterus. 

 vd = vas deferens. 

 m = yolk-gland. 



