NOTARBARTOLO-ni-SCIARA NATl'RAl. HISTORY OV MORULA 



especially the tissue at the bases of claspers, of 

 the larger males appeared swollen and congested 

 in May and June, and some of the skin had as- 

 sumed a pink coloration. Similar observations in 

 carcharhinid and odontaspid sharks have been 

 linked with mating activities (Springer 1960; 

 Gilmore et al. 1983). 



The ovaries in M. thursfoni are paired, elon- 

 gated organs located inside the pleuroperitoneal 

 cavity, analogously to the testes, and are con- 

 nected to a large epigonal organ. Eggs are pro- 

 duced within the germinative epithelium. The 

 largest eggs were found at the anterior end of the 

 ovary. Only the left ovary develops and is func- 

 tional, whereas the size and aspect of the right 

 ovary remains comparable with those of the im- 

 mature stage. Asymmetry is also present in the 

 oviducts, the left uterus being usually the largest 

 in mature females. It consists of a voluminous, 

 thick-walled expansion of the lower tract of the 

 oviduct; its lumen is lined with a highly devel- 



oped epithelium consisting of elongated, flattened 

 villi (trophonemata), a well-known mobulid (Gill 

 1908; Setna and Sarangdhar 1950; Wourms 1977) 

 and rhinopterid (Schwartz 1966; Smith and Mer- 

 riner 1986) feature. In several instances both 

 uteri were found to contain a viscous, whitish or 

 greenish substance. Oviducts open separately 

 into the cloaca. A progression of sexual maturity 

 in female mobulids was evident from the exam- 

 ined ovary's developmental condition. In the im- 

 mature female the germinative epithelium is a 

 narrow, leaf-shaped band, tapering at both ends, 

 located opposite to the mesovarium (facing the 

 center of the cavity) along the ovary's longitudi- 

 nal axis. In mature females the germinative ep- 

 ithelium takes over most of the ovary's ventral 

 side, making room for the mature ova. To deter- 

 mine the size at maturity of female M. thurstoni, 

 the diameter of the largest ovarian egg was plot- 

 ted against DW (19 specimens. Fig. 4). An egg 

 growth plateau was not evident, because data on 



Figure 3. — Relationship between clasper size and body size 

 in Mobula thurstoni. 



50 



I 40 



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 Q. £ 20 

 OT ^ 



< s 



i 10 



• ••mtn«l fluid pr»««nl 

 O ••minal fluid aba«nl 





y 



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to 



500 1000 1500 



DISC WIDTH (mm) 



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Figure 4. — Relationship between size of largest ovum and 

 body size in Mobula thurstoni. 



1000 1500 



DISC WIDTH (mm) 



2000 



51 



