CHAPTER 7 



THE EYES OF ROTIFERS (WHEEL ANIMALCULES) 



In tracing the homology of different groups of animals it often appears 

 that although the adult forms of these have undergone marked differentia- 

 tion along divergent lines, so that they show little resemblance to each 

 other, yet the larval forms are so like that the possibility of the two groups 

 having sprung from a common ancestor is at once apparent. In this 



lliiu-- ape 



po.orc. 



Fig. 56. — Trochophore Larva of a Rotifer showing Apical Plate and Eye- 

 spot, OF WHICH THERE ARE USUALLY TWO. (AFTER HATSCHEK.) 



An. : anus. nephr. : nephridium. 



ap. c. : apical cilia. oes. : oesophagus. 



ap. pi. : apical plate. oc. : eye-spot. 



int.: intestine. po.or.c: post-oral circlet of cilia. 



m. : mouth. pr. or. c. : preoral circlet of cilia. 



n. : nerve. st. : stomach. 



respect the study of the larva or trochophore of the rotifers is of the very 

 greatest interest. This trochophore (Fig. 56) is a pear-like structure 

 which in many respects resembles the Tornaria of Balanoglossus (Fig. 124, 

 Chap. 13, p. 170, and Fig. 125, Chap. 14, p. 172). Thus in the 

 trochophore we recognize a pear-shaped organism with the broad end 



