The Embryology of Heterodontus japonicus 719 



During the season of 1900, the work was of a preliminary nature; considerable time was 

 spent in exploring the sea bottom in search of favorable localities for collecting. Since the 

 table in Dean's notebook contains no entries later than July 6, none of the entries could 

 apply to specimens taken during the summer of 1900. Therefore it seems likely that all 

 the entries in the table apply to one season only; the spring and summer of 1901. How- 

 ever this may be, we have no individual records for embryos collected earlier than April 

 nor later than July 6 in any year, despite Dean's statement that collecting was carried out 

 for him ''at various intervals throughout the year". It is known to Dean's colleagues that 

 collecting for him was carried on at various times during his absences from Japan. That 

 some records are missing is obvious. I have found no records for individual embryos 

 aside from those in Dean's table. The missing records include all stages over 35 mm. total 

 length, excepting a few newly hatched. 



Text'figure 43. 

 Diagrams representing stages in the early development of Heterodontus japorncus. A, blastula stage shortly 

 after deposition of the egg, which occurs chiefly in March and April. The egg is drawn as seen from above, 

 with the upper pole, which Dean calls the animal pole, in the center. The germinal disc appears near 

 the equator in the upper part of the figure. B and C, stages in gastrulation and early embryo-formation 



found most frequently in May. 



From drawings left by Bashford Dean 



Of the 135 embryos listed by Dean, 14 were taken in April, 59 in May, 20 in June, 

 and 42 in July (first week only). This distribution does not quite accord with Dean's 

 statement, recorded in his manuscript, that "The divers brought in the maximum number 

 of eggs during April and May", unless some records for April are missing. From the 

 original records it appears that most of the 14 eggs collected during April were in late 

 cleavage, or blastula, stages (Text-figure 43a). This, according to Dean, implies that 

 the eggs were newly spawned. A very few had reached an early gastrula stage, and 

 (significantly) one was in the hatching stage. During May, a great majority of the 

 59 eggs collected were in gastrula stages (Text-figures 43b and 43c), but there was 

 a sprinkling of eggs in both younger and older stages. A few yolk sacs bore embryos old 

 enough to perform wriggling movements. In June, with only 20 embryos, the range of 



