PRATT REPRODUCTION IN BLUE SHARKS 



The ovary is composed of hundreds of follicles in a 

 dense stroma of connective tissue. In the blue 

 shark, follicles are contained in a single layer of 

 generative tissue which blankets the ova as they 

 develop. 



The ovary of a full-term 243 cm gravid female, 

 with 60 embryos "in utero," contained over 1,000 

 follicles (Figure 13). Although the average 

 number of embryos seldom exceeds 54 (Bigelow 

 and Schroeder 1948), this ovary contained 123 ripe 

 eggs from 6 to 20 mm in diameter. Also present 

 was a similar number of corpora lutea of various 

 sizes, ranging from 1.2 to 7.5 mm in diameter, 

 presumably from the generation then contained in 

 the uterus. So-called corpora lutea are also found 

 in the developing ovaries of immature blue 

 sharks. It is likely that the 123 large ova consti- 

 tute the next generation of 50-60 embryos, and 

 that the balance would be reabsorbed. This would 

 explain the presence of 120 corpora lutea found in 

 the ovary of this female which, as determined by 

 her size, was at the end of her first pregnancy. The 

 next generation is recruited from those follicles 

 currently in the 0.3-3.5 mm size class. No follicles 

 were present between 3.5 and 6.9 mm diameter. 



The epigonal organ is a paired straplike organ 

 that extends the length of the peritoneal cavity. 

 The anterior end is suspended from the dorsal 

 body wall just behind the heart cavity near the 

 origin of the liver and extends caudally, supported 

 by a thin mesentery, to the insertion of the rectal 



FOLLICLE SIZE (mm) 



FIOURE 13. — Size/frequency population of ovarian follicles in a 

 243 cm gravid blue shark. A. 202 follicle subsample of an esti- 

 mated 1.000 follicles in the ovary, grouped in 1-0 mm intervals. 

 B. 124 maturing ova grouped in 10 mm intervals. 



gland. The organ is 3 cm in diameter in the central 

 body cavity and gradually expands and flattens to 

 10-15 cm wide and 2-3 cm thick at each end. 

 Matthews (1950) speculated that this is the site of 

 erythrocyte production in elasmobranchs. It 

 serves no reproductive function other than sup- 

 porting the ovary. 



Ostium 



The ostium is the anterior opening of the oviduct 

 located at the forward end of the peritoneal cavity. 

 It is a 10 mm long membranous funnel which 

 bifurcates into the right and left oviducts. Lying 

 between the ostium and the oviducal gland, the 

 oviducts are firm white cylindrical tubes 10 mm in 

 diameter. They traverse the curved mesentery 

 that supports the liver to become attached to the 

 dorsal peritoneal wall where the oviduct joins the 

 oviducal gland. 



Oviducal Gland and Isthmus 



Approximately 80 cm from the ostium the ovi- 

 duct expands to form the oviducal gland. It is 

 heart-shaped, 3-4 cm in diameter, and 4-5 cm long. 

 The oviducal glands of the adult female blue shark 

 are small relative to other elasmobranchs. Exter- 

 nally, each is a symmetrical snow-white organ, 

 with two short horns on the lateral anterior sur- 

 faces. The structure and function of this gland are 

 discussed in a later section. 



As it leaves the oviducal gland, the oviduct re- 

 sumes its original diameter of 10 mm, but is now 

 lined with longitudinal furrows and folds of tissue. 

 This part of the oviduct is termed the isthmus 

 (Figure 12) and runs for 15-20 cm from the ovi- 

 ducal gland to the uterus. 



Uterus and Vagina 



At the end of the isthmus the oviducts expand in 

 diameter to 2 or 3 cm in nongravid adults and join 

 the paired uteri (Figure 12). Each uterus is 50-60 

 cm long and supported by a mesometrium. In fish 

 that have pupped recently the uterus is flaccid and 

 much larger (5-15 cm diameter). Even at its small- 

 est diameter the uterus of adult females is always 

 thick-walled and oval in cross section. The uteri 

 unite at their posterior end to form the common 

 vagina. The length of the vagina is about 15 cm. Its 

 distal end is demarcated by the hymen, a circular 

 transverse fold. The hymen separates the vagina 



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