296 



ANIMAL LIFE 



FIG. 331. Amphibian egg of two 

 cells with the furrow forming to 

 divide it into four cells. Photo- 

 graph through the microscope 

 enlarging twenty diameters. 



changes in form and structure. 

 The egg of the jellyfish does 

 not produce directly the free- 

 swimming parent form, but 

 develops into what is known as 

 the hydra tube (Fig. 203), which 

 after a time by transverse di- 

 vision gives rise to several 

 jellyfish. The egg of a tape- 

 worm eaten by an animal 

 becomes in a favorable host 

 a somewhat globular body 

 known as the cysticercus or 

 larva. In this condition it may live for months or 

 possibly years until the flesh containing it is eaten 

 by the proper host 

 for the develop- 

 ment into the com- 

 plete tape form. The 

 larva of the cat's 

 tapeworm lives in the 

 mouse, and the tape- 

 worm of the dog is a 

 cysticercus in the rab- 

 bit (Figs. 184, 185). 



Among the insects 

 very marked differ- 

 ences in form occur 

 during the life of 



FIG. 332. Frog's eggs from three to ten hours 



the yOUng. In SOme old. All stages from four cells to thirty-two 



i , ,-, cells may be noted. Photograph enlarged 



orders, such as the four times. 



