22 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



found on adult female carcharhinids and are gen- 

 erally restricted to the dorsal surfaces between 

 the two dorsal fins. These are never present on 

 males or immature females and are obviously 

 produced during courtship. Scars or wounds are 

 not always present on gravid females or at least 

 are not always detectable but were found on 

 about half the gra'vid E. milberti taken at 

 Salerno. The coexistence of old and completely 

 healed scars with fresh scars on some females is 

 one bit of evidence that female E. mnhei'ti pro- 

 duce more than one litter of pups in a lifetime. 

 All available evidence points to the month of 

 June as the time of maximum mating activity of 

 E. milberti in southeastern Florida waters. It 

 has- already been pointed out that 4nales were 

 rarely taken during the month of June when 

 mating activity is assumed to be at a peak. There 

 is some evidence from catches that the males were 

 present in substantial numbers at that time. 

 From 3 to 5 percent of the catches of the better 

 fishermen at Salerno, who kept their hooks very 

 sharp, were snagged sharks; that is, the sharks 

 were caught by hooks in the fins or tails or occa- 

 sionally in other parts of the body but not in the 

 ^noiuth. More males were (jauglit in thik wa'y dur- 

 ing June than were iTOoked by mourh. 



Development of the embryo ''^■ 



In E. milbei'fi. as in other carcharhinids, it is 

 presumed that fertilization occurs after the large 

 egg leaves the single functional ovary. It is also 

 presumed that fertilization occurs before the egg 

 has been moved through a shell gland. Shell 

 glands are located near the anterior end of each 

 of the two functional oviducts. In passing 

 through the shell-gland area of an oviduct, a 

 single egg is enveloped by a diaphanous tubelike 

 shell capable of great expansion to accommodate 

 the growth of the embryo to a very large size. 

 The nutrient material from the egg yolk is suffi- 

 cient only to provide for early growth of the 

 embryo and to supplement nutrient materials 

 necessary for intermediate growth. The means 

 by which nourishment is supplied to the growing 

 embryos probably varies in different species of 

 carcharhinids, but in species of Eulamia, three 

 principal methods appear to be involved. In 

 addition to that sui)plied by the yolk some ab- 

 sorption of nutrient material from fluids in the 



oviducts may be assumed to take place. This 

 would appear to be necessary to provide sufficient 

 material to carry the embryo to a length of about 

 12 inches at which length the pseudoplacenta is 

 formed from the yolk sac. 



M^ observationKtHi the^mbryology of the sand- 

 bar shark are limited to general notes on the ex- 

 ternal appearance of the eggs and embryos at 

 several stages during development. 



The spherical, unfertilized eggs in the single 

 functional ovary reach a diameter of 1 to li/i 

 inches. In winter and early spring, large num- 

 liers of adult females not carrying embryos were 

 fomul to have developing eggs 1/2 to 3^ inch in 

 diameter in the ovaries. In a few instances, fe- 

 males taken in July and August were found with 

 eggs of maximum size in the ovaries as well a& 

 fertilized eggs in the oviducts. In the greatest 

 disparity of development noted, there were two 

 large yellow eggs remaining in the functional 

 ovary while embryos in the oviducts ranged from 

 less than 6 mm. to 10 mm. in length. 



A female 7niJherfi. 6 feet 7 inches long collected 

 off Salerno on July 2, 1948, in 25 fathoms, was 

 typical of a series taken in early July of that., 

 year. This female contained 10 egg cases, 5 in 

 each oviduct ; no large eggs remained in the fimc- 

 tional ovaiy. Each stringlike egg case was about 

 120 centimeters long, with thin membranous, 

 amber-colored, transparent walls. A single yolk 

 was contained in one expanded oval section of 

 each egg case. The expanded section, approxi- 

 mately 6 cm. long, was located about 10 to 12 cm. 

 from one end of the egg case. This section also 

 contained a clear fluid in each of 8 of the egg 

 cases that had developing embryos 9 to 13 mm. 

 long. The remaining 2 egg cases, one anteriorly ' 

 in each oviduct, contained milky fluid and there 

 was no evidence of fertilization nor development 

 of the single egg yolk contained in each. The 

 section of the egg case occupied by the embryo, 

 spherical yolk, and clear fluid was held in shape 

 by two longitudinal folds and by folded constric- 

 tions of the egg-case membrane at either end. 

 Xlie eo-fT case could, however, be unfolded and ex- 

 panded with relatively light internal pressure. 



The egg case surrounds the embryo until birth 

 and unfolds or stretches to accommodate the de- 

 veloping embryo. "When the embryo reaches full 

 term the pseudoplacental mass extends outside of 



