332 



ZOOLOGY 



the first. The mouth in this case is always placed between the two 

 circlets on the ventral side (Fig. 2(57), so that the inner or anterior 

 circlet is pre-oral and corresponds with the chief ciliary band 



E.Hex a rthro 



3.Trocho s f>h a e r a 



Fig. 270. — Typical forms of Rotifer a. In 1, a shows the outer form, 6 the muscular system. 

 a. anus ; br. brain ; A c 2 . ciliary circlets ; cl. cloaca ; d. gl. digestive gland ; d. I. dorsal limb ; 

 e. eye-spot; I. I., I. I', lateral limbs; in, muscles; mtk, mouth; nph. nephridial tube; 

 ov. ovary ; ph. pharynx ; ,«. sense-organ ; v. I. ventral limb. (After Hudson and Gosse 

 (1 and 2) and Korschelt and Heider (3).) 



of a trochosphere larva, while the outer or posterior circlet corre- 

 sponds with the post-oral band found in many worm-larvae; In the 

 curious globular Trochosphwra (Fig. 270, 3) there is a single 

 equatorial circlet, which is pre-oral, and a few post-oral cilia : here 

 the correspondence with the typical worm-larva is singularly 



