ANIMALS OF UNCERTAIN RELATIONSHIPS 67 
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. 
70. 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. 42) 
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. 92), they 
were earlier associated in the same group; but an examina- 
tion of their internal organization inclines many zoologists 
