ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 323 



This sinus is usually injected if the needle of the syringe is simply plunged into the 

 liver at random. The liver admits of considerable vascular distension. The tubules 

 may be so close together as to obliterate, or almost obliterate, the intervening blood 

 spaces, or the latter, if congested, force the tubules apart and form relatively large 

 channels. 



(B.) Second, as regards the histology of the liver tubules. The Myxinoid liver is a 

 simple tubular or racemose gland, in which the tubules end blindly and form no net- 

 works. Microscopically there is only one kind of tubule. I have searched in vain in 

 my serial sections for any glandular tissue which might constitute a histological pancreas. 

 The liver is enclosed in the usual serous and fibrous coats, the latter with long nuclei ; 

 but no trabeculse are dispatched internally to ramify among the liver tubules. In fact, 

 the liver has only an extremely slight connective-tissue framework. Some of the large 

 superficial blood-vessels, however, are invested by fibrous tissue continuous with that of 

 the external fibrous coat. 



The liver tubules are circular or oval in transverse section, and possess a very thin 

 non-cellular basement membrane. The central cavity, varying with the state of activity 

 of the tubule, may be large and irregular, small and round, or apparently wanting 

 altogether. Under the hig-hest magnification the free border has a well-defined margin 

 outlined by chromophilous granules like exceedingly minute nuclei. The diameter of 

 the tubules varies from 32 to 78 m — average 56 fi ; height of the cells from 8 to 28 m 

 — average 17 m;* diameter of the cavity from 4 to 44 m (Holm gives 3 to 8 m) ; 

 the number of cells seen in a transverse section of a tubule is from 4 to 15, average 

 number 8 to 9 (Braus says 4 to 6 and Holm 5 to 10). 



The cytoplasm of the liver cells may be very vacuolated. Large intracellular cavities 

 may occur which themselves open into the larger lumina of the tubules. Intercellular 

 canaliculi or bile capillaries may be very numerous and striking, so that in transverse 

 section a star-shaped cavity is seen. The cells of the whole liver may be thus vacuo- 

 lated, but here and there small aggregations of tubules are found with solid cytoplasm 

 and slightly larger nuclei. These are in sharp contrast with the surrounding vacuo- 

 lated cells, owing to their naturally taking on a deeper stain. 



Small patches of adipose tissue are to be seen scattered among the liver tubules. 



The nuclei of the liver cells are spherical, with well-marked reticular chromatin, and 

 are obvious diff"erentially staining nucleolus. They measure from 5 to 10 /x, but the 

 larger sizes are the more frequent. Occasional mitoses, of the type described by the 

 ScHREiNERS in other Myxine tissues, may be observed. 



In thick sections we notice that the superficial tubules are looser, have larger cavities 

 and more vacuolated cytoplasm, and are not so packed together as are the more central 

 tubules. 



The structure of the liver of Myxine has been investigated by Braus, who used 



* According to Braus, 30 fi. 



