316 PROFESSOR FRANK J. COLE 



is devoid of the glassy and granular mucous cells. Near the cloacal opening, however, 

 and in the dorsal chamber of the cloaca,* the two latter become extremely numerous — 

 in fact much more so than they are in the neighbouring skin. Posterior to the anus, 

 the lining of the entire cloaca, and even the urinary papilla, contain both kinds of 

 raucous cells. 



Suhmueosa. — The stratum compactum behaves as at the anterior boundary, and 

 passes gradually into the dense and more deeply staining fibrous submucosa of the 

 hind-gut. In the 19 -cm. Hag the submucosa of the posterior extremity of the mid- 

 gut is almost replaced by large blood spaces. The characteristic blood sinus in the 

 stratum compactum immediately underneath the mucosa can be traced no further back 

 than the change in the epithelium. The lymphoid cells are not present at the extreme 

 end of the submucosa of the mid-gut, and the adipose areolar section of the submucosa 

 dies away somewhat in front of the epithelial boundary. 



Musculature. — In the sections of the 25-cm. Hag a new tissue appears in the hind- 

 gut. The unstriated musculature of the mid-gut disappears, and is replaced by a 

 primitive tissue resembling an extremely simple form of cartilage, unlike, however, any 

 definitive cartilage of Myxine. It encircles the whole of the hind-gut, exclusive of the 

 posterior extension of the body cavity and of the segmental ducts, and recalls the thin 

 sheet of cartilage described by Ayers and Jackson in the wall of the cloaca of 

 Bdellostoma (cp. my Part I., p. 786). In the sections of the 19-cm. Hag this tissue is 

 not present, and its place is occupied by a well-developed and undoubted unstriated 

 circular musculature, but there are indications posteriorly of its replacement by the 

 connective tissue. 



Maas failed to find any glassy or granular cells in the cloacal epithelium, although 

 he says they reappear in the " anal " slit itself He also describes a muscularis 

 mucosae, a statement I am unable to confirm. Schreiner, like myself, finds both kinds 

 of mucous cell in the cloaca. 



The height of the mucous epithelium in the different regions of the gut may now 

 be given. The measurements are in /x. The nasal tube at the opening is 48 ; it 

 rises to 100 and sinks to 60 at the posterior end. In the naso-pharyngeal duct the 

 epithelium is only 32 at the anterior end, but it gradually deepens as it approaches its 

 oral aperture, where it is about 80. In the mouth, up to the posterior extremity 

 of the velum, the height varies from 80 to 140, but is more frequently about 100, the 

 lower figure, however, being more usual behind. In the pre-branchial gut the epithehum 

 is very constant, and measures almost invariably 100. In the branchial gut it drops from 

 100 to 80. It rises in the region of the constrictor cardise to 100 and 120, but falls 

 to 80 on the first entry of the gut into the abdominal coelome. In the abdominal gut 

 the figures vary from 102 to IGO, the commonest measurement being 140, whilst at the 

 posterior end it is 120. 



* i.n. ill the region of Burnk's "anal slime gland." 



