DEVELOPMENT OF THE PORBEAGLE SHARK. 1 69 



The uterine portion of the parental oviduct is thick-walled and 

 highly vascular ; its inner Avails, moreover, are thrown into deep 

 folds which have a glandular appearance. There is no evidence, 

 however, that the uterine wall secretes a nutrient material. 

 The uteri of specimens examined by Dr, Williamson contained, 

 as he assures me, no substance apart from the embryos them- 

 selves. 8wenander (7) found in the uterus of his specimen forty 

 pieces of material, which proved to be groups of eggs surrounded 

 by a common membrane. The portion of both oviducts imme- 

 diately above the uterus in specimen F contained matter 

 i-esembling the contents of the yolk-stomach, the lumen of the 

 shell-gland was replete with it, and it was also present in the 

 uppermost portions of the oviducts as far as their source ; the 

 skinny content, as might be expected, was not found above 

 the level of the shell-gland. The ovaries themselves were large 

 but contained no ripe ova; their contents much resembled in 

 consistency the matrix in the yolk-stomach, but was darker 

 in colour owing apparently to the accumulation of blood. 



Not onl)^ did the matter in the yolk-stomach resemble that in 

 all parts of the oviduct as regards physical properties, but a. 

 general chemical analysis conducted in the school laboratoiy 

 revealed no outstanding difference in this respect. 



Similar material was found in the mouth and oesophagus of 

 each of the embryos of the F and H groups. 



The only conclusion acceptable on tliis evidence is that nutrient 

 material is derived from the ovary in the form of immature eggs 

 or partially degenerate ovarian tissue — that this is taken up by 

 the oviduct, is partial!}' or completely covered with a thin mem- 

 brane in the shell-gland, and is passed tlience into the uterus, 

 where it is swallowed by the embrj'os. 



The contents of the spiral intestine a.re of a uniform semi-fluid 

 consistency and of a greenish colour; they have, in fact, every 

 appearance of having undergone the process of digestion. The 

 rectum also contains greenish matter of a somewhat darker 

 shade, and veiy slight compression of the trunk of the embryo 

 (before dissection) causes this feecal matter to exude from the 

 cloaca. 



These observations seem to show that food supplied by the 

 ovary is taken into the alimentary system of the embryo through 

 the mouth and digested in the manner characteristic of free- 

 living animals. Owing to the sedentary nature of the embryo 

 there is little wastage of tissue to repair ; and, since the supply 

 exceeds the demand, a vast surplus of potential food accnmidates 

 in the cardiac portion of the stomach. Whether all the waste 

 products of digestion normally accumulate in the intestine of the 

 embryo until birth, or whether a poi-tion of them is voided into 

 the maternal uterus requires investigation. If fsecal matter finds 

 its way into the uterus it must be got rid of in some way. The 

 passage of the utei'us to the cloaca is short and wide; it is possible 



