FISHERY BULLETIN: VOL. 81, NO. 1 



FULL SIZE 

 OVARIAN EGG 



ANTERIOR 



I cm 



POSTERIOR 



OVARY 



Figure 3.— "Ripe" ovary of an Atlantic sharpnose shark. The 

 ovary contains ca. 20 mm ova that are ready to ovulate. 



an equal number of ova enter both oviducts, 

 although in some instances greatly dispropor- 

 tionate numbers of embryos were found between 

 right and left uteri. The eggs move through the 

 oviducts to the oviducal gland where fertilization 

 probably takes place. The oviducal gland (Fig. 4) 

 in the Atlantic sharpnose shark is a paired struc- 

 ture located at the forward end of the oviduct. 

 The oviducal glands are the source of the egg 

 case, and in some sharks the glands may be the 



cranial oviduct 



lumen opening 

 caudal oviduct 



ANTERIOR 



POSTERIOR 



1.0mm 



Figure 4.— Diagram of an oviducal gland taken from a mature 

 female Atlantic sharpnose shark. 



site of long-term sperm storage (Pratt 1979). 

 Viable sperm can be found within the lumen of 

 those tubules within the gland which secretes the 

 egg shell (Wourms 1977). As no histological sec- 

 tions of adult sharpnose sharks' oviducal glands 

 were prepared, the question of sperm storage in 

 sharpnose sharks remains unresolved. Prasad 

 (1944), however, noted the presence of spermato- 

 zoa in the oviducal glands of Scoliodon sorra- 

 kowah, a closely related Indian Ocean species. 

 This observation suggests that the oviducal gland 

 may have at least a short-term storage capacity. 

 After moving through the oviducal gland the 

 fertilized eggs then move to the uterus where 

 they become implanted in depressions in the 

 uterine wall. At this point the eggs are found en- 

 cased in a thin, yellowish shell with pointed ends 

 (Bigelow and Schroeder 1948). Within the uterus 

 the eggs are elongate, averaging about 18 mm 

 wide and about 32 mm long. Fertilization is ap- 

 parently very efficient since in examination of 

 315 embryos only two unfertile eggs were noted 

 (0.6%). 



Placentation and Structure of 

 the Umbilical Cord 



During the first 2.5 to 3.0 mo of gestation, the 

 Atlantic sharpnose shark embryos depend upon 

 the yolk sac for nourishment. After about 3 mo 

 the yolk sac has become intimately associated 

 with the uterine wall to form a yolk-sac placenta. 

 October embryos, i.e., 3 mo old, were ca. 16 to 20 

 cm and had well-developed placentas with little 

 yolk material remaining. By November, 4 mo 

 into gestation, embryos were 19 to 23 cm long 

 and no yolk material remained in the placenta. 

 In a related Indian Ocean species, Scoliodon sor- 

 rakowah, Mahadevan (1940) described a very 

 thick vascularized area of the uterine wall, re- 

 ferred to as a trophonematous cup, which forms 

 to receive the yolk sac of the foetus. This vascu- 

 larized area was also noted in the Atlantic sharp- 

 nose shark. 



Development of the umbilical cord closely par- 

 allels placentation. The umbilical cord is con- 

 nected on the embryo's ventral surface in the 

 midpectoral region. Very early in development 

 the umbilical cord is virtually naked. By the time 

 the embryos have grown to about 6.0 cm TL the 

 umbilical cord has developed many knoblike ap- 

 pendages which give it a "pipe-cleaner" appear- 

 ance. The appendages are about 1 mm long, and 

 terminate in one or a cluster of several grapelike 



64 



