The Embryology of Chlamydoselachus 561 



retained in the uteri during further development. I was told by the director, Dr. A. G. 

 Mayor, that this was his understanding, but after these years I cannot recall if this was 

 his personal observation. I was never fortunate in procuring large embryos nor small 

 free-swimming young. Development is slow and the advent of the hurricane season led 

 to the closing of the laboratory late in July of each year before the slowdeveloping eggs 

 had gone far enough for the embryos to break out of their shells. 



The young and growing fishes in the uteri of these two viviparous sharks must have 

 oxygen. If sea water could penetrate the cloaca and into the uteri, it might provide this 

 need. The nurse shark has a wide cloaca and the oviducal opening into it will sometimes 

 admit "three or four fingers bunched into one mass", as my notes read in one case, and in 

 them it is also recorded that a female Ginglymostoma hung up by the tail had the common 

 oviducal opening measuring 1.5 in. in diameter. The opening must be this large to admit 

 the outward passage of the large empty egg shells even if crumpled. Furthermore, I have 

 opened a uterine egg of the nurse shark and on tasting the perivitelline fluid have found 

 this salty. The embryo was very young. 



I unwittingly performed another experiment which demonstrated that the egg 

 capsule of Ginglymostoma is permeable to sea water. I took an egg capsule with its 

 lively embryo out of the uterus of a just-killed female, cut a window in the capsule over 

 the embryo, cleared out all the perivitelline fluid that I could and replaced it with mo- 

 lecular magnesium sulfate in order to anesthetize the embryo. The egg was then unthink- 

 ingly placed in a dish of sea water which did not cover the window. Twenty-two hours 

 later the little shark was about as lively as ever. The sea water had penetrated the egg 

 shell by osmosis and had so diluted the anesthetic solution that the embryo still lived. 



There seems to be little doubt that the embryos of Ginglymostoma may get oxygen 

 from the sea water which may come into the uterus through the dilated cloaca and the 

 large oviducal openings. No experiments such as those above have been performed on 

 Chlamydoselachus, but Dr. Smith tells me that the cloaca is open in his preserved speci- 

 mens and that the right oviducal opening even when hardened in formalin will sometimes 

 admit a man's thumb. So one may conjecture that sea water invades the uterine cavity of 

 Chlamydoselachus and bathes the eggs. Thus the embryo could get oxygen from this 

 water. 



On the whole it seems quite probable that the young of both sharks may receive some 

 oxygen by difi^usion from the uterine wall into the fluids surrounding the embryo. Fur- 

 thermore, from my knowledge of uterine gestation in other sharks and in various rays, I 

 am strongly of the opinion that the uterine wall in both Chlamydoselachus and Ginglymos' 

 toma secretes Hquid food materials to nourish the young after they are freed from the egg 

 capsules. As shown in Figure 34, plate III, and Figure 43, plate IV, the embryos of 

 Chlamydoselachus have short external gills, gills far shorter than I have found in the 

 young of some viviparous sharks and particularly of various rays. Presumably the young 

 of Ginglymostoyna also have such gills. The long external gills of embryos of rays and of 

 other sharks, when bathed in the uterine fluid, may take in not only oxygen but mineral 



