304 J. H. ASH WORTH. 



Pig. 30. — Thin transverse section (3 (i thick) of the end of a ventro-lateral 

 mesentery, to which three very young sperm sacs are attached. In the one 

 to the right the primitive genital cell has divided into four, three only of 

 which are visible. X 500. 



Pig. 31. — Section of a sperm sac a little older than the largest one shown 

 in the preceding figure. The central cavity containing a coagulum has now 

 appeared. X 150. 

 Tig. 32. — Section of an older sperm sac. x 150. 



Pig. 33. — Section of a mesentery, on the end of which is a sperm sac in 

 which the central cavity, having reached its greatest size, is now being 

 encroached upon by the heads of ripening spermatozoa. Note that the 

 spermatozoa are surrounded by a thin film of mesogloea (represented in the 

 distal part of the sac by the line inside the endoderm), and by an endodermic 

 follicle, some of the cells of which contain from two to five nuclei, x 150. 

 Pig. 34. — Uipe spermatozoa. 



Pig. 34a. — From a section of the stomodscum, through the dorsal portion 

 of which spermatozoa are escaping. Only the head and point of attachment 

 of the tail are seen. X 800. 



Pig. 34b. — An entire ripe spermatozoon from a teased preparation of a large 

 sperm sac. X 800. 



Pig. 35. — Cells from thin sections (4 n thick) of large sperm sacs, to show 

 the two to five nuclei which may be present in each, x 800. 



Pig. 36.— Transverse section of a ventral mesentery of a young polyp '95 

 mm. long (V in table, p. 284 ; see also PI. 24, fig. 5). The section is taken 

 about "5 mm. below the lower end of the stomodeeum. Note the already 

 diiferentiated primitive genital cells migrating from the endoderm into the 

 mesoglcea, and the short finger-shaped flagella of three of the endoderm cells. 

 X 500. 



Pig. 37. — View of a colony of Heteroxenia Elizabeths. The colony 

 was split in two longitudinally and the proximal half drawn, hence only half 

 the summit of the stem is seen. Note the autozooids with pinnate tentacles, 

 and the very numerous short siphonozooids with short rounded tentacles, 

 and also the young polyps growing near the edge of the summit, x 3. 



Pig. 38. — View of the youngest autozooid on the colony, '64 mm. long 

 (A 1 in table, p. 287). The specimen has been flattened out by pressure 

 against the side of the bottle which contained the colony. Note the long 

 finger-shaped tentacles ; the right proximal one is slightly indented near the 

 tip, but the others have simple rounded ends. The stomodseum is indicated. 

 X 40. 



Pig. 39. — The largest siphonozooid on the colony (S 7, fig. 38, and table, 

 p. 288). The short simple tentacles, the stomodseum, and the two dorsal 

 mesenteries witii tiieir filaments are shown. X 15. 



