208 



COMPARATIVE ZOOLOGY. 



Coral, when hatched, has six pairs of partitions; after- 

 wards, the spaces are divided by six more pairs; then 

 twelve intermediate pairs are introduced; next, twenty- 

 four, and so on. The embryonic Star -fish has a long 

 body, with six arms on a side, in one end of which the 

 young Star -fish is developed. Soon the twelve -armed 

 body is absorbed, and the young animal is of age. 

 Worms are continually growing by the addition of new 

 segments. Nearly all Insects undergo complete metamor- 

 phosis, i. e., exhibit four distinct stages of existence — egg, 

 larva, pupa, and imago. The worm-like larva 117 may be 

 called a locomotive-egg. It has little resemblance to the 

 parent in structure or habits, eating and growing rapidly. 

 Then it enters the pupa state, wrapping itself in a cocoon, 

 or case, and remaining apparently dead till new organs 

 are developed; when it escapes a perfect winged Insect, 



Fig. 172.— Butterfly in the Imago, Pupa, and Larva States. 



or imago. 118 Wings never exist externally in the larva; 

 and some Insects which undergo no apparent metamor- 

 phosis, as Lice, are wingless. The Grasshopper develops 

 from the young larva to the winged adult without chang- 



