23 G WILLIAM BATE SON. 



Fig, 38. — Transverse section tlirougli the anterior end of the collar of a 

 larva between Stages F and G (slightly older than the preceding). (Obj. D, 

 00. 2). The nervous system is shown still continuous with the skin in this 

 region. 



Fig. 39. — Transverse section through the same larva as Fig. 38, taken 

 somewhat behind the section there represented. (Obj. D, oc. 2.) The 

 nervous system is here detached from the skin, to become continuous with it 

 again posteriorly. 



Fig. 40. — A diagram representing the arrangement of the parts as seen in 

 a median horizontal longitudinal section through a larva at Stage E. In this, 

 as in Fig. 41, the epiblast is of the medium shade, the hypoblast dark, and the 

 mesoblast light. 



Fig. 41. — Diagram of a longitudinal vertical section through a larva between 

 Stages F and G. The letter B indicates the dorsal side ; shading as in Fig. 40. 

 The anal perforation is here represented in order to show its eventual position. 

 It would not, however, be found until Stage G is reached. The relations of 

 the closed prseoral body cavity and of the nervous system to other structures 

 are here shown. 



