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Bashford Dean Memorial Volume 



light on this obscure problem, let us now examine the uterus of that ovoviviparous shark 

 whose reproduction most nearly parallels that of Chlamydoselachus. 



The tropical shallow-water nurse shark, Ginglymostoma cirratum, carries in each 

 greatly dilated uterus as many as 21 huge thick-shelled eggs like that shown in natural 

 size in Text-figure 16. The inner wall of each uterus is made up of circumferential bands 

 of hems or plaits overlapping like the shingles on a roof. The plaits are 5 or 6 mm. wide 

 and are highly vascularized — "as red as a piece of fresh-cut beefsteak" my notes read. 



Text-figure 16 

 The egg case (140 mm. long), egg, and embryo of the ovoviviparous nurse shark, Ginglymostoma 

 cirratum — in natural size. Note the left, older, more finished looking end of the capsule and the 

 larger, blunter, younger right end. The yolk blastopore is seen just to the right of the tail of 



the embryo. 



Photograph by Alfred Goldsborough Mayor. 



We have no statement of the collectors that embryos and their yolks are found in the 

 uteri of Chlamydoselachus free of their shells, but it is evident that an embryo even as 

 relatively young as that shown in Figure 11, plate I, or as old a one as that shown in 

 color in Figure 49, plate V, has thrown off its heavy egg capsule. These large broken 

 capsules could not be carried in the uterus without hurt to the delicate embryos. They 

 must be thrown out into the sea. Similar reasoning must be applied to similar conditions 

 in the nurse shark and its embryos enclosed in a larger and thicker egg shell. 



The boatmen at the laboratory of the Carnegie Institution of Washington at Tortu- 

 gas, Florida, where my studies were made, were all Florida and Bahama men, well ac- 

 quainted with the nurse shark. They all told me that when the young are pretty well 

 developed, they break out of the shells, and these latter are cast out while the embryos are 



