ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 309 



structure by the new methods of solution and digestion, using caustic alkali and 

 pancreatic extract. I shall therefore confine myself to a general statement of the 

 anatomy of the gut, supplemented by such new details as are necessary to amplify and 

 elucidate the work already accomplished. 



The gut of Myxine passes straight from mouth to anus. There are no obvious 

 divisions into stomach, duodenum, and intestine. It is characterised by one very 

 striking and unique feature. The mucous epithelium from the mouth to the entry of 

 the gut into the abdominal cavity — that is, rather more than a third of its entire length 

 — exhibits the peculiar and characteristic structure of the epidermis. The obvious 

 explanation of this is that the whole of the lining of the anterior part of the gut is 

 stomodseal in origin, but this we know to be not the case. The only other possible 

 explanation, therefore — which is in fact no explanation at all — is that we have here a 

 remarkable example of what is known as convergence. There can be no doubt that 

 this anterior third of the gut represents an enormously elongated pharynx. It is 

 pharyngeal in position in the embryo, but the interpolation of the club muscle during 

 development detaches the gill-bearing region of the gut from the mouth, and results in 

 the curiously posterior position of the gills in the adult. 



There are two types of gut structure in Myxine. These we may call the pharyngeal 

 gut and the abdominal gut. The former stretches from the mouth to the entrance of 

 the gut into the abdominal cavity, and the latter continues the gut to the cloaca. 



As an example of the 'pharyngeal gut or " (esophagus " we may take what Maas 

 calls the branchial gut. The mucous epithelium, which is many-layered, has just the 

 character of the outer skin, and possesses in abundance both the clear glassy and the 

 granular slime cells characteristic of the epidermis. Maas distinguishes a stratum 

 corneum and a stratum Malpighi, but, unless these terms are to acquire a new meaning, 

 I do not see how they can be applied in this case. He also describes a muscularis 

 mucosae which goes far into the folds ; but I find no trace whatever of this, nor, 

 apparently, does Schreiner. The submucosa is dense and fibrous, and with many 

 lacunar blood spaces. According to Maas, however, it consists of loose, very uniform, 

 reticular cells with no lacunae. Externally there is an obvious circular musculature of 

 unstriated fibres. These fibres course among the dense connective tissue of the sub- 

 mucosa in its peripheral region. There are only a few isolated fibres, but they are easily 

 seen, and they course right round the gut, taking no account of the folds of the mucosa. 



According to Schreiner, the mucosa has a basal membrane and exhibits no trans- 

 verse folds in the " oesophagus," but these are certainly present in the branchial region. 

 The superficial cells of the mucous epithelium give the slime reaction, and have a thin 

 homogeneous cuticle. He finds a coiled thread in the granular slime cells, exactly as in 

 the corresponding cells in the epidermis. I am unable to confirm this, in which I agree 

 with Haack. There are numerous mitoses in the mucosa. , 



In the abdominal gut, it is stated by Maas that the folds of the mucosa have less 

 projection, although this is not so in my preparations. He finds the ventral folds are 



TRANS. ROY. SOC. EDIN., VOL. XLIX. PART IL (NO. 3). 40 



