in.] METAMORPHOSES OF INSECTS. 61 



Among the Ophiurans also we find two well-marked 

 types of development. Some passing through meta- 

 morphoses, while others, as for instance Ophiopholis 

 bellis, " is developed very much after the method of 

 Asteracanthion Mulleri, without passing through the 

 Plutean stage." 1 



Even in the same species of Echinoderrn the degree 

 of development attained by the larva differs to a 

 certain extent according to the temperature, the 

 supply of food, &c. Thus in Comatula, specimens 

 which are liberally supplied with sea-water, and kept 

 warm, hurry as it were through their early stages, and 

 the free larva becomes distorted by the growing 

 Pentacrinus (see Fig. 43), almost before it has attained 

 its perfect form. On the other hand, under less 

 favourable conditions, if the temperature is low and 

 food less abundant, the early stages are prolonged, 

 the larva is longer lived, and reaches a much higher 

 degree of independent development. Similar dif- 

 ferences occur in the development of other animals, 

 as for instance, in the Hydroids, 2 and among the in- 

 sects themselves, in Flies ; 3 and it is obvious that these 

 facts throw much light on the nature and origin of 

 the metamorphoses of insects, which subject we 

 shall now proceed to consider. 



1 A. Agassiz, Embryology of Echinoderms, p. 1 8. 



2 Hincks. British Hydroid Zoophytes, pp. 120-147. 



3 Zeits. fur Wiss. Zool. 1864, p. 228. 



