THE ENTEROPNBUSTA. 63 



network, sf., is formed superficially by the anastomosing heads, each of 

 the nodes being the head of a cell. Obj. D, oc. 2. 



Fig. 77 [a and b). — Cells of preparation similar to Fig. 76, more separated, 

 (c) Spindle-shaped cells from lower layer of skin, probably broken off from 

 cells resembling a and b. Obj. F, oc. 2. 



Fig. 78. — Transverse section through middle third of the central nervous 

 system of B. Kowalevskii. Obj. D, oc. 2. 



Fig. 79. — Longitudinal section of skin of posterior third of proboscis of 

 B. Kowalevskii. Obj. D, oc. 2. 



Fig. 80. — Horizontal section through the skin of the collar of B. 

 Kowalevskii. Obj, D, oc. 2. 



Fig. 81. — Vertical section of the above. Obj. D, oc. 3. 



Fig. 82. — Section taken tangentially to the flexure of the body of young 

 B. Kowalevskii (8, g. s.), showing the spinal folding in the digestive region 

 of the gut. Obj. B, oc. 2. 



Fig. 83. — Longitudinal section of the tail of young B. Kowalevskii 

 (4, ff. s.). Obj. D, oc. 2. 



Fig. 84. — Longitudinal section through the wall of the posterior region of 

 the branchial sac, showing the relations of the valves and skeletons of the 

 gills (B. Kowalevskii, W, g. s.). Obj. A, oc. 2. 



Fig. 85.^ — ^Diagrams of successive stages in the development of the gill- 

 slits of B. Kowalevskii. 



Fig. 86. — Macerated preparation of the gill-skeleton of B. Kowalevskii. 

 Obj. A, oc. 2. 



Fig. 87. — Longitudinal section of adjacent valve and gill-bar of B. 

 Kowalevskii. Obj. D, oc. 2. 



Fig. 88. — Longitudinal horizontal section through atrial cavity of B. 

 Kowalevskii in the plane of the opening into it of the collar funnel and 

 first gill-slit. Obj. B, oc. 2. 



Fig. 89. — Transverse section through the back of the branchial sac of 

 B. Kowalevskii (10, g. s.). Obj. A, oc. 2. 



Fig. 90. — Vertical section of pharyngeal wall of B. minulus. Obj. D, 

 oc. 3. 



Fig. 91. — Vertical section of one of the lateral ridges, separating the 

 branchial sac from the lower part of the branchial region. Obj. A, oc. 2. 



Pie. 92. (a) Transverse section of the dorsal ridge of the branchial region 



of B. Kowalevskii. {b) The same of B. minutus. Obj. A, oc. 2. 



Pie. 93. Transverse section through the junction of a liver saccule with 



the gut, through the back of the adjacent saccule (B. minutus). Obj. A, 

 00.2. 



