420 



Wilson: 



[Vol. VI. 



VII. General History of the Metamorphosis. , 



As a considerable time may elapse before the publication of 

 the second part of this paper, it seems desirable to give a 

 sketch of the structure and metamorphosis of the larva in 

 order to make clear its rather peculiar relations to the adult 

 body and to justify my orientation of the early stages. 



After the disappearance of the ventral depression the larva 

 becomes perfectly spherical, and this form is retained up to the 

 time when the stomodaeal arc closes (a stage slightly later than 

 Fig. 80, 18 hrs.). After the occurrence of this event the lower 

 hemisphere begins to change its shape, becoming slightly flat- 

 tened in front (Fig. 82), so that the most prominent point is 

 somewhat behind the lower pole, which lies about in the centre 

 of the pigment-area. As this marks the first step in the meta- 

 morphosis, the general structure of the larva at this stage may 

 be briefly described. The entomeres are still undivided and 



