84 ANIMAL STUDIES 



by the sticky secretion of the foot, to sweep the food-par- 

 ticles down into the mouth. Through the walls of the 

 transparent body such substances are seen to pass into the 

 stomach, where they are rapidly hammered or rasped into 

 a pulp by the action of several teeth located there. In 

 the absence of a circulatory system the absorbed food is 

 conveyed by the fluid of the body-cavity, which also con- 

 veys the wastes to the delicate kidneys. Several other 

 features of their organization are of much interest, espe- 

 cially to the zoologist, who believes that he gains from 

 their simple structure some ideas of the ancestors of the 

 modern worms, mollusks, and their allies. During the 

 summer the rotifers lay two sizes of "summer eggs," 

 which are remarkable for developing without fertilization. 

 The large size give rise to females, the smaller to males, the 

 latter appearing when the conditions commence to be un- 

 favorable. The " winter eggs," fertilized by the males and 

 covered with a firm shell, are able for prolonged periods to 

 withstand freezing, drought, or transportation by the wind. 

 The adults also are able under the same adverse conditions 

 to surround themselves with a firm protective membrane 

 and to exist for at least a year. Once again in the presence 

 of moisture the shell dissolves, and in a surprisingly short 

 space of time they emerge, apparently none the worse for 

 the prolonged period of quiescence. 



80. Gephyrea. There is a comparatively large group of 

 worm-like organisms, over one hundred species in all, which 

 at present hold a rather unsettled position in the animal 

 kingdom. Some of the more common forms (Fig. 48) 

 living in the cracks of rocks or buried in the sand, usually 

 in shallow tide pools along the seashore, have a spindle- 

 shaped body terminated at one end by a circlet of tentacles 

 which surround the mouth. On account of their external 

 resemblance to many of the sea-cucumbers (Fig. 95), they 

 were earlier associated in the same group ; but an examina- 

 tion of their internal organization inclines many zoologists 



