ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 311 



On the other hand, I find them in all parts of the layer, and round veins of all sizes. 

 They form a kind of pulp compared by Maas with the splenic tissue of higher 

 vertebrates. He states that the lymphoid cells resemble the free colourless corpuscles 

 of the blood, to which they undoubtedly give rise : not, however, to the red corpuscles, 

 which always lie free in the vessels and lacunae, and the early stages of which are 

 never found in the connective-tissue framework of the gut. On the other hand, the 

 early stages of the leucocytes occur in the framework, and the lymphoid tissue of the 

 gut represents their principal source, the associated veins always containing an excess 

 of leucocytes. It is, however, difficult to believe that the lymphoid tissue performs 

 this function only. It is so extensive a structure that some further explanation of its 

 presence must be sought. 



SoHREiNER describes mitoses both in the epithelial and glandular cells of the 

 abdominal mucosa. Gland cells are never formed from epithelial cells, but are always 

 derived from pre-existing gland cells. The nucleus migrates towards the lumen before 

 it divides, and this explains why the mitoses are always found outside the nuclear zone. 

 ScHREiNER finds the lumen end of the cell rich in fat droplets, which diminish when 

 the animal has been kept in an aquarium some days without food. This part of the 

 cell gives the slime reaction with appropriate stains. I agree with Schreiner that the 

 thick free edging is in two parts — a proximal, binding the cells together ; and a striated 

 distal, of elements corresponding to the individual cells. 



Both Maas and Schreiner state that the abdominal gut is uniform in structure 

 from one end to the other. I have carefully explored the entire length of this section 

 of the gut, and agree to the above statement with, however, this proviso : I have 

 generally found that, either immediately or shortly following the bile duct, the lumen 

 of the abdominal gut undergoes expansion — largely owing to the fact that the mucosa 

 is at this point without folds and almost smooth. The entire wall of the gut, in fact, 

 is here very thin. On the other hand, the above features are not associated with any 

 histological peculiarity. Nevertheless, this region must have some significance. 

 Further, at the hind end of the abdominal gut, the mucosa is thrown into numerous 

 secondary folds, in which the suhmucosa takes no part. 



Such are the characters of the two types of gut structure found in Myxine. We may 

 now consider the various stretches of the gut in more detail. 



Maas distinguishes the following regions in the gut of Myxine, apart from the 

 mouth : — 



1. Branchial gut — up to the opening of the ductus cesophago-cutaneus 30 



2. True oesophagus — up to the entrance of the gut into the body cavity 3 '5 



3. Stomach— up to the opening of the bile duct . . . . 2*5 



4. Mid-gut or abdominal gut 60-5 



5. Hind-gut 3*5 



100 



* These figures are not Maas', but are calculated from data given by him. 



