202 



ZOOLOGY 



often degenerate. The summer eggs are of two kinds — large and small — and 

 develop parthenogenetically. The large eggs produce females and the small, 

 males. The winter eggs have a thick shell and are believed to require fertiliza- 

 tion in order to develop. They rest during the winter and in the spring develop 

 into females. Development is direct. The adult condition in the Rotifers sug- 

 gests the larval {trochophore) condition in some Annelida. There are some traces 



Fig. 95. 



i--s,.f 



Pig. gs. Diagram of a sagittal section of a Rotifer. 6, brain; bl.^ excretory bladder; c, cloaca; 

 the common opening of digestive and reproductive organs; co, coelom; e, eyespot; ex, excretory 

 canal; /. flame cells; /.£., foot gland; ft., foot; g, gut; m, mouth; m.f., longitudinal muscle fibres. 

 mx, mastax; 0, ovary; ^h., pharynx; s.g., salivary gland; (, tentacle; ir, trochus, or cilia-bearing disc. 



Questions on the figure. — What sets of organs and functions are indicated in 

 the diagram? Does this seem a lower or higher form than the other types studied 

 in this chapter? What are your grounds for your answer? What indications of 

 segmentation are represented in the figure? Is the mastax in the stomodaeum or 

 mesenteron? Where do the various authors classify Rotifers? 



