478 R. M. PACE. 



and pharynx. The neuro-rmiscular cord (iV.3/.) is in process of development. 

 The niesendoderm forms a solid mass in tiie posterior part of the larva. 

 Viewed from the left side, x 225. 



Fig. 63 a. — Longitudinal section through the larva at a slightly later stage 

 than tiiat illustrated in Fig. 62, viewed from the left side, Themesendodermic 

 mass has now become hollowed out to form the stomach. Viewed from the 

 left side, x 225. 



Fig. 63 b. — Transverse section through the region of the pharynx of a larva 

 of tlie same age as tliat siiown in Fig. 63 a. Two bands of tissue (*), which 

 may possibly represent the true mesoderm, are budding off from the mesendo- 

 dermic mass, x 225. 



Fig. 64. — Transverse section of a larva older than that which is represented 

 in Fig. 63 ; the plane of section passing through the stomach, internal sac, and 

 pharynx. X 225. 



Fig. 65 a-c. — Sections of mature larvae. 



a. Longitudinal section of a larva, viewed from the right side, in which 

 the larval organs are all fully developed. The pharynx and internal sac 

 have lost the globules which were present in earlier stages ; the pyriform 

 organ now consists of the " systeme glandulaire superieure " {S.G.') witli 

 the " fossette superieure" {Fs.) and the "systeme glandulaire inlerieure," 

 (S.G.") only the right side of which is visible: the " fente cilice" is not 

 shown. The stomach has become very elongated. The ciliated crown (C.) 

 is now visible. (From a drawing by Dr. S. F. Harmer.) 



b. Transverse section of the larva in a plane passing through the stomach and 

 internal sac. The two bands of tissue which appear to be budding off from the 

 mesendoderm are again noticeable. X 225. 



c. Transverse section passing through the stomach and pharynx of the larva. 

 X 225. 



Fig. 66. — Transverse section of a larva in which degeneration has com- 

 menced. The walls of the internal sac have become much thickened and the 

 protoplasm near the opening to the exterior has assumed a granular appear- 

 ance. The ciliated crown now consists of a single row of large cells. The 

 stomacii has vanished, and the mesendoderm is represented only by scattered 

 nuclei and yolk spherules, among which lie numerous muscle-fibres, x 225. 



