THE SYSTEMATIC ANATOMY OF A FCETAL SEA-LEOPARD. 239 



these to have been formed. When a section of the pancreas stained with hsema- 

 toxylin is examined, it appears that the cells lining the alveoli are not characterised 

 by the deeply-staining outer zone which is so marked a feature in the pancreas 

 of the armadillo ; moreover, the nuclei lie at the outer or attached borders of 

 the cells. 



(v.) The spleen. — In minute structure, the spleen presents the following features : — 



(a) Externally, a somewhat dense fibrous capsule, in which also unstriped muscle 



cells are undergoing development. 



(b) Trabeculse passing from the capsule into the substance of the gland, and 



forming a network in the interior : near the surface some large arteries 

 may be seen passing in, more especially in the vicinity of the hilus, and 

 corresponding venous branches are emerging. 



(c) The bulk of the organ is made up of a mass of erythrocytes, erythroblasts, 



and lymphocytes ; here and there cells suggesting the splenic cells of the 

 adult organ may be seen, but giant-cells are apparently not present. A 

 section taken through the splenic artery and vein with the blood contents 

 of these vessels shows quite clearly that the vein contains many more 

 lymphocytes than the artery, a feature which indicates that the lymphoid 

 function of the spleen is already established ; whilst the presence of ery- 

 throblasts in fairly large numbers in the spleen-pulp leads to the inference 

 that hsemogenesis is also a splenic function at this stage — a point which 

 is well established in the case of the rabbit and some other mammals. 



No Malpighian corpuscles are to be seen in a section of the organ, but in some 

 places the lymphocytes seem to be more densely aggregated than in others, with an 

 indication of a small artery in their neighbourhood : these masses are not, however, 

 well defined. 



(vi.) The kidneys and adrenal bodies (PI. XXII. figs. 1 and 2). — At this stage the 

 kidney presents histogenetic features which correspond fairly closely with those seen 

 in the kidney of a four-months human foetus ; that is to say, each renal pyramid 

 when sectioned in a plane passing through the cortex and the apex of the papilla is 

 seen to be made up of the following parts : — ■ 



(a) A cortical zone, in the outermost layer of which are to be seen the di- 

 chotomously branched endings of the tubules derived from the ingrowth 

 into the metanephros of the diverticulum from the Wolffian duct ; in many 

 of them the ampullary portions are continued into a coiled tubule — cut 

 across many times and in various planes — the first or proximal convoluted 

 tubule. At a somewhat deeper region of the cortex, the first set of 

 Malpighian capsules are to be seen, these being relatively large as com- 

 pared with those arising later : no sign of Henle's tube is as yet evident, 



