DEPARTMENT OF MARINE BIOLOGY. 149 



the hinder edges of their pectorals much frayed, battered, and seemingly bit- 

 ten, while the fins of males were later found to be intact. When the breeding 

 habits were studied the matter became clear. Fertilization is internal, and 

 as a preliminary step to the process of copulation the male grasps the hinder 

 edge of the pectoral fin of the female with his mouth. It seems to be a mat- 

 ter of indifference which fin he lays hold of. His mouth being small and his 

 teeth weak, the female not infrequently breaks away from him ; hence the 

 torn and scarred condition of her pectorals. The male at length subdues the 

 female and, throwing her on her back with his body above, inserts his claspers 

 into the lateral pockets of her cloaca and transmits the seminal fluid. 



Dissection of the female reveals some interesting structures. The ovary 

 is single and seemingly median, but study of several 15-inch specimens shows 

 that this is the right ovary, the left having become atrophied. The right 

 ovary with its great eggs has become enormously developed and has come to 

 lie in the median line. These eggs, 2 to 2.5 inches in diameter, are somewhat 

 flattened, yellow in color, and perfectly fluid. The oviducts are paired and 

 in the anterior third each has an enlargement, the shell gland. Just behind 

 each shell gland the oviduct is enlarged to form the uterus ; but this, instead 

 of being of uniform size throughout, as the writer has found in Scoliodon 

 terrccnovcB, Sphyrna tiburo, and other sharks, or swollen into a shape ap- 

 proaching semispherical, as in Dasyatis say, D. hastata, Pteroplatea maclura, 

 and other rays, is enlarged throughout, but on the ventral side is developed 

 into a conical enlargement containing the bulk of the eggs. 



The inner surface of the uterus has the lining raised in folds or plaits about 

 0.5 inch wide. These are arranged in circular fashion, overlapping each 

 other, like shingles on a roof. These plaits are not smooth, but have the sur- 

 face broken up into short prolongations. Evidently we have here a means 

 for oxygenating and feeding the young after they have broken out of the 

 shell, but are still retained in the maternal uterus. 



The large eggs are contained in large horny capsules, larger and thicker 

 than any selachian egg-shells which the writer has yet studied. The average 

 length of normal eggs is about 130 mm., girth 180 mm. Most of the eggs 

 have blunted terminals which at times form stumpy prolongations, and in a 

 few instances filaments as long as the egg-case proper are found, but these 

 are readily detached. 



The early blastoderms are exceedingly small, so much so that they would 

 hardly be noticed but for their darker color, contrasting with the yellow yolk. 

 Very old blastoderms have a projecting lip or edge which may be lifted from 

 the underlying yolk by a needle. At one place an inpushing of the blasto- 

 derm rim is found and at the head of this the embryo is formed. About one- 

 third of the series of embryos necessary for a study of the development has 

 been obtained. Old embryos have long external gills, deep red in color. 

 The filaments projecting from the spiracles are very short and of an intense 

 red color. 



The eggs taken from the uterus of the mother will continue their develop- 

 ment in running salt-water. A number with late embryos were left at the 

 laboratory at Tortugas on my departure on July 25. These were to have 

 been preserved at intervals by one of the laboratory men, but one of the eggs 

 went bad and as a result all died. How the embryos burst the shells is as yet 

 unknown. To complete the series, further collections will have to be made 

 during the months of June and August. 



Sharks of three other species were taken and dissected; one 10 feet 10 

 inches in length was caught in Key West Harbor; careful measurements 



