302 Bashford Dean Memorial Volume 



BREEDING SEASON 



On this subject we have information from but two men, Nishikawa and Dean. The 

 former (1898) says "The breeding season is spring, extending from about the end of March 

 to the beginning of June." Presumably Nishikawa means that this is the season of copulation 

 and fertilization. Nishikawa obtained an egg having on it a blastoderm 1.3 mm. in 

 diameter. Unfortunately he gives no date for this— it could not have been many days, 

 possibly not many hours old. He also obtained an egg in the blastula stage, and a gastrula 

 3 mm. in length. Of slightly older forms he writes that "The youngest batch of embryos 

 was obtained from a specimen 170 cm. long, which was brought to the University [of 

 Tokyo?] on the 26th of May 1896. There were six embryos 32, 35, 43, 48, 50, and 60 mm. 

 long respectively." From our knowledge of shark embryology, we judge that these eggs 

 were fertili2;ed at various times during that spring. 



From Dean's scattered notes we have gleaned the following data. His earliest 

 material consisted of three blastulae obtained on April 10. Had Nishikawa dated his 

 embryos we could check his dates against Dean's. On April 25, 1903, Dean's collector 

 obtained for him (from two females) twelve eggs with embryos, stages not noted. Two 

 days later the same collector got a female with two embryos, but their stages were not 

 noted. Again he records that on May 25 five large eggs were obtained, but nothing is 

 said about embryos. 



From the data given there can be little doubt that the breeding season (the time of 

 copulation and fertilization) begins in the early spring — in March and April. Nishikawa 

 says that it extends until June, but one queries if it may not extend longer, even if it may 

 not last throughout the year as there is reason to believe that it does in many sharks. 



PERIOD OF GESTATION 



That gestation lasts for a year or more, we judge in part from the huge size attained 

 by the eggs. Dean speaks of some ovarian eggs as 60 mm. in diameter and of others measur' 

 ing 30x70 mm. That these ovarian eggs are unripe is shown by the fact that he records 

 (but did not preserve) an embryo 390 mm. (15.3 in.) long, on a yolk-sac measuring 70x100 

 mm., while another embryo of 331 mm. (13 in.) sat on a yolk-sac measuring 100x111 mm. 

 Furthermore, Nishikawa speaks of eggs found in the oviduct as measuring "each 110-112 

 mm. long." Also, Nishikawa recorded living eggs (not yolk-sacs), which he says were 

 ellipsoidal in form, measuring 65-75 mm. in shortest diameter and 102-124 mm. in longest 

 diameter. Apparently it was the egg-cases, not the eggs proper, that were measured, but 

 one can judge, from his figures (our Text-figures 2 and 24), the size of the eggs contained 

 therein. 



The second thing leading to the belief that gestation lasts for a year or more is the 

 great size of some embryos taken from the uterus. Dean notes "1905, early Jan., embrs. 

 of 11.5, 15.5, 20 mm." Under date of Apr. 25, he lists embryos of "16.5, 17-5, 18.5, 19.5, 

 20.5, 21, 25 cm." (165-250 mm., 6.5-9.8 in.). Again "4 embrs., large, taken about May 1, 

 1905." And last of all "1905, Bt. in Tokyo, June 20, 317.5 mm., 331 (yolk-sac 100x111), 



