300 Prof. Wood-Mftson and Mi. Alr.x-k. On /// 



oviduct iu the nature of the mucous membrane. In many it is raised 

 into villi. Glands are much developed. The relation of this di . 

 of the oviduct to the egg or to the embryo that originates ther 

 is a tolerably various one. Least intimate is it in the oviparous 

 Selachii (Raja and Scyllium) : only furnishing the egg-case. In 

 others (Spinax, Acanthias, Scymnus), a shell is also developed, but 

 only for a short time, and the embryo afterwards lies free in the 

 uterus. Here come those Selachians in which there is no longer any 

 shell at all developed, and from this circumstance results the nutritive 

 connexion of the foetus with the uterine wall by the intermediation 

 of the yolk-sac." 



This passage, although it clearly de6nes the well-known function* 

 of the Selachian uterine mncosa, on the one hand of secreting an 

 egg-case, and on the other hand of forming a vascular nutritive con- 

 nexion with the modified yolk-sac of the embryo, makes only a vague 

 allusion to another modification of function : namely, the secretii 

 by special uterine glands of a nutritive fluid which might be absorl 

 or ingested by the developing embryo. 



Leydig also ('Handbuch der Histologie,' Ed. 1857, p. 51! 

 describes the vascular uterine villi of Acanthias, Spinax, Scynu 

 and Trygon, though without discussing their relation to the egg 

 to the embryo. He says : " In the Selachians the mucous metnbrai 

 (of the uterus) either appears smooth and possessing only zig-: 

 longitudinal folds (Scyllium, for example), or it bears mnch-develo] 

 villi (Acanthias vulgaris, Spinax niger, Scymnus lichia, Trygonpastinaca] 

 These villi are placed sometimes (Acanthias rulgaris, Scymntu lichia} 

 in very regular longitudinal rows which cease towards the end of 

 uterus, and pass into leaf-like longitudinal folds ; or, as in Ti 

 pastinaca, they are so crowded together that nothing more of the 

 of the mucous membrane of the uterus appears. The villi possess 

 exceedingly rich vascular supply : there are to be distinguished 

 them at most two stronger vessels which interlace and run into 

 another at the end of the villus, and between the two a close-mesh< 

 vascular network. These vessels are in the gravid uterus dis- 

 tinguished by a proportionately very thick circular muscular layer." 

 There are figures (p. 318, Ed. 1857) of " the uterus of Trygon, opened, 

 in order to show the villi " ; and of " a bit of the uterine mncosa of 

 Spinax, somewhat more than the natural size," showing the much- 

 developed villi, which are represented as two- to three-branched. 



The great comparative anatomist Johannes Miiller, in his exhaus- 

 tive paper : " Ueber den glatten Hai des Aristoteles " (' Abhand. Ak. 

 Wiss. Berlin,' 1840, p. 188), reviews more completely the state of 

 knowledge up to that date of the Selachian uterine structures which, 

 quite apart from the secretion of egg-coverings or the formation of 

 yolk-sac placentae, are concerned in the elaboration of secretions 



