III.] 



METAMORPHOSES OF INSECTS. 



55 



processes, are supported by calcareous rods. This 

 larva swims by means of minute vibratile hairs, or 

 ciliae. It has a mouth, stomach, and in fact a well- 

 defined alimentary canal ; but no nerves or other in- 

 ternal organs 'have yet been discovered in it. After 

 swimming about in this condition for a while, it 

 begins to show signs of change. An involution of the 

 integument takes place on one side of the back, and 



FIG. 39. Larva of Echino-cidaris, seen from above x & (after Muller). 



continues to deepen till it reaches a mass or store of 

 what is called blastema, or the raw material of the 

 animal body. This blastema then begins to change, 

 and gradually assumes the form of the perfect 

 Echinoderm. 1 



1 Huxley, Introduction to the Classification of Animals, p. 45. 



