191 1] Louis Hiissakof and William H. Welker 221 



VII. SUMMARY OF GENERAL CONCLUSIONS 



The egg capsules of the skate and the Port Jackson shark con- 

 sist, in the main, of materlals that resemble keratin superficially, 

 but which differ in essential respects from that substance. 



The keratinoid siibstances obtained from the two types of tgg 

 capsules are ahke in some respects, e. g., in their insolubiHty in 

 water, alcohol, ether and Chloroform. They are different, however, 

 in other regards. Differences were observed in their behavior in 

 alkaline and acid media, the product from the Raja capsules being 

 somevvhat more soluble in alkaline reagents, that from Heterodontus 

 was more soluble in concentrated acid media. 



It is obvious that this keratinoid material imparts to the tgg 

 capsules the mechanical protective qualities which are characteristic 

 of them. 



The tgg capsules of these fishes contain pigments which, in alka- 

 line Solution, are dark red in color. Though somewhat different in 

 tinctorial effects, the coloring matters bear close resemblance to each 

 other, as was shown by their similar behavior in various qualitative 

 tests. Possibly they are as nearly the same chemically as bilirubin 

 and biliverdin. 



Neither the exact chemical nature of the pigments, nor their 

 functional significance, has as yet been determined. That the pig- 

 ments are melanins seems probable. 



The writers are deeply indebted to Prof. William J. Gies for 

 much valuable advice given them during the progress of this inves- 

 tigation. 



VIII. EXPLANATION OF FIGURES 



Fig. I. — Egg capsule of the Skate {Raja eritmcea) ; natural size. Long Island. 



Fig. 2. — Egg capsule of the Port Jackson Shark {Heterodontus philippi) ; X i- 

 Japan. (After Waite.) 



