FISHERY BULLETIN: VOL 79, NO. 4 



ovophagous. Horny infertile eggs are deposited in 

 each oviduct and the embryo consumes these as 

 development proceeds (Cadenat 1956; Gubanov 

 1972). Figures 15 and 16 show the embryos and 

 the infertile eggs removed from the oviducts of 

 specimen SHG-A2. Curiously, Gubanov (1979) 

 claimed that the eggs of the bigeye thresher differ 

 considerably from those of the common thresher. 

 However, the eggs shown in our Figure lib appear 

 almost exactly like those shown in Gubanov's 

 figure 1. Yet the eggs shown in Gubanov's figure 1 

 were said to be characteristic of the common 

 thresher only. A possible explanation of this 

 discrepancy is that Gubanov's figures 1 and 2 

 actually represent nutritive and fertile eggs, 

 which might be similar in both species. 



Most sharks do not acquire functional teeth 

 until they reach a size close to that at parturition. 

 However, both of our immature fetuses (Figure 

 15) had fully functional teeth, which is quite 

 unusual among sharks. Perhaps the early forma- 

 tion of teeth aids the fetal bigeye thresher 

 in cannabalizing potential siblings. Yet, fetal 

 pelagic thresher A. pelagicus does not acquire 

 functional teeth until it reaches considerably 

 larger size than our two bigeye thresher fetuses. 



As is often the case in odontaspidids and 1am- 

 nids, the bigeye and other threshers produce only 

 two well-developed offspring per pregnancy. 

 While Guitart Manday (1975) mentioned one or 

 two embryos in each oviduct the usual number is a 

 single fetus in each oviduct (Nakamura 1935; 



Figure 15. — Embryos removed from the specimen shown in Figures 1 and 2. As shown, they are approximately 206 

 mm TL and are probably in the first trimester of development. Photo: S. Gruber. 



Figure 16.— Infertile, homy eggs of A I opias superciliosus (SHG-A2) found in the oviducts 

 along with the embryos. Thresher embryos are thought to consume the nutritive, yolk- 

 filled eggs during development (ovophagy). Photo: F. Karrenburg. 



634 



