The Embryology of Chlamydoselachus 559 



But in any case, we are sure that, in some few instances, Chlamydoselachus does have 

 both oviducts functional. 



Here then is confirmation of Smith's statement (1937) — "In view of the great varia' 

 biHty found in many other organs of Chlamydoselachus, one should not be surprised if 

 examination of additional material [Dean's 26 female specimens] should reveal cases in 

 which the genital organs of the left side, or both sides, are functional''. And all through 

 his work. Smith points out generalised or primitive structures in Chlamydoselachus in 

 consonance with the lowly position assigned it in the scale of shark life. Then again he 

 finds highly specialized structures. 



Chlamydoselachus is in process of becoming viviparous by getting rid of its primitive 

 keratinoid egg shell — it has almost gotten rid of the hold'fast processes. Then further to 

 make possible this viviparity in a small and narrow body cavity, it has almost achieved 

 unilaterality in the functioning of its reproductive organs. 



For comparison, evidence will later be presented to demonstrate that in certain 

 higher viviparous sharks and in certain rays (highly specialized elasmobranchs) the 

 unilaterality found imperfectly expressed in Chlamydoselachus has come to full fruition. 



There is now to be considered certain indefinite evidence referred to above — the 

 question whether the embryos of Chlamydoselachus are nourished by secretions from 

 the wall of the maternal uterus. 



Do Embryos Receive Nutriment From the Uterine Wall? 



On this point Hawkes (1907) writes of the enlarged (uterine) portion of the right 

 oviduct as follows : 



This region in addition to being enlarged has folded walls, in which occur one large 

 and several small areas of dilated blood vessels. The largest blood plexus occupies about 

 one-third of the right side of the oviduct. In connection with each plexus, on its dorsal side 

 the oviducal wall is thickened over an area which equals the plexus in length and breadth. 

 The enlarged vessels apparently supplied these thickened areas. The condition of the 

 oviduct thus described suggests that this portion of the oviduct acts as a functional uterus. 



Smith had hoped by study of our specimens to throw more light upon the internal 

 structure of the uterus as described by Hawkes. But he had little success. He notes, 

 however, (1937, p. 447) that — ''In its enlarged state, on the right sides of my adult 

 specimens, the so'called uterus has thin walls, a velvety inner surface and a fairly rich 

 blood supply. The mucous membrane is not sufficiently well preserved to permit a study 

 of the finer structure". 



To anyone with a firsthand knowledge of the structure and functioning of the uterine 

 wall of viviparous sharks and rays, these findings are very significant. From a mere 

 glance at Figure 49, plate V, it is apparent that there will never be a yolk-sac placenta 

 connection between embryo and mother in Chlaynydoselachus. It the uterus nourishes 

 the embryo, this must be accomplished in some other way. In the hope of getting some 



