ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 337 



of a single layer of cells, but that of the terminal duct of many layers of cells ; (2) 

 that the two epithelia bevel into each other exactly as they do at the mid- and 

 hind-gut boundary (cp. description of gut) ; and (3) that the glassy and granular 

 mucous cells characteristic of the epidermis may occur at any part of the terminal 

 duct. In the 19 -cm. Hag the two terminal ducts open separately and symmetrically, 

 but in the 25-cm. specimen the openings were asymmetrical, as already described in 

 the mature animal. It seems natural to conclude that the segmental duct terminates 

 at the anterior border of the constrictor cloacae in the sinus-like swelling, and that the 

 terminal duct is simply an integumentary (epidermal) pocket. It must, however, not 

 be forgotten that on similar grounds we should have to regard the whole of the 

 pharyngeal gut as epidermal, and this we know to be contrary to fact. 



In one respect the description given above is directly contrary to the following 

 statement by Burne. He says : " Now in the adult myxinoid the ureters do not 

 imperceptibly pass into the cloacal chamber, as they do into the urogenital sinus of 

 the lamprey, but open upon a raised papilla ; upon the margin of the ureteric opening, 

 the epithelium changes its character — inside, it is sirmlar to that lining the rest 

 of the ureter; outside, it is epidermic'' [italics m.ine]. 



In the transverse sections of the 19-cm. Hag the rectum fuses ventrally with the 

 abdominal wall at the anterior ventral margin of the sphincter cloacae, and further 

 back the whole fuses with the skin at the boundary between mid- and hind-guts. 

 The gut is now connected with the roof of the abdominal cavity by the deep median 

 dorsal mesentery. Then the striated sphincter cloacas rises round and over the roof 

 of the gut and splits the body cavity into two portions, placed one over the other, and 

 each divided by a median vertical partition — the posterior continuation of the 

 mesentery. The dorsal pair of cavities soon die away, the left one first. The ventral 

 pair one naturally expected to open posteriorly at the genital pore. The median 

 mesenteric partition, first of all, becomes imperfect ventrally, but the dorsal portion 

 remains suspended from the roof of the cavity almost to its posterior extremity. The 

 cavity becomes narrowed and surrounded by a dense cellular connective tissue, which 

 finally fuses with the upper section of the cloaca, but the lumen ends blindly ivithout 

 opening anywhere. There was, therefore, no porus genitalis in this specimen, nor the 

 slightest trace of the anal slime sac described by Burne. In the series of longitudinal 

 sections of the 25-cm. Hag the constrictor cloacae does not partition the body cavity 

 as above described, but passes entirely above it. The posterior blind extremity of the 

 body cavity bends downwards and backwards, and approaches a blind epidermal cloacal 

 pocket. The two are separated by a plug of cellular connective tissue. A close 

 examination of this plug reveals phagocytic operations in its central core, and there is 

 no doubt that in this specimen the genital pore was in the act of breaking through. 

 This, of course, may happen at diff"erent sizes according to sex and conditions of 

 maturity. In this example also there were no signs of the anal slime sac. Hence the 

 genital or abdominal pore of Myxine is to be found only in the mature animal. It 



