SECT, i] PHYSICO-CHEMICAL SYSTEM 351 



simultaneously showed that the eggs of the catfish, which are un- 

 doubtedly bottom ova, have large oil-globules. Another theory was 

 put forward by van Bambeke, who believed that the oil-globule was 

 a special form of yolk, and of a purely nutritional significance. Prince 

 criticised this view on the ground that the oil persists in the yolk 

 after the liberation of the embryo from the egg-membrane, and travels 

 beneath it as it swims about. This would not, however, negative the 

 possibility that the oil was used for larval rather than embryonic 

 nourishment. Van Bambeke' s claim that a protoplasmic thread 

 passes from the oil-globule to the germinal disc was almost completely 

 disproved by van Beneden. His and Miescher, examining the oil 

 histochemically, found that it only stained very slowly with osmic 

 acid, and therefore differed profoundly from the yolk, and, although 

 it was soluble in ether, it contained no more than a trace of phos- 

 phorus. It is remarkable that the oil has never been subjected to 

 a proper chemical examination, especially in view of the extensive 

 zoological literature on it. What we know of its properties faintly 

 hints, perhaps, that it may be a hydrocarbon like squalene, and the 

 whole question, indeed, holds out great possibilities for physiological 

 as well as chemical work. The oil must readily dissolve lipochromes, 

 for the pink pigment of the salmonoids is found in it. Prince's own 

 theory was that the globule was a constituent of ancestral significance, 

 a vestige from the time when, as Balfour showed, the teleostean yolk was 

 very much larger than it is now. The nutrition view is probably the best. 

 The lipoids and sterols of the eggs of the lower animals are very 

 little known, and their further study is much to be desired. Page in 

 1923 described a sterol — asteriasterol — which he isolated from the 

 eggs of Asterias forbesii and which turned out to be closely related to, 

 though not identical with, ordinary- cholesterol; the eggs of Arenicola 

 cristata, on the contrary, yielded a sterol absolutely identical with 

 the well-known substance as it occurs in mammals. Ten years pre- 

 viously, in a less accurate study, Matthews had failed to find any 

 cholesterol at all in the eggs of Asterias forbesii, though he had been 

 able to isolate some from those of Arbacia punctata. From the former 

 he got a jecorin-like substance, containing 10 per cent, of glucos- 

 amine, which was probably a mixture of kephalin, cerebrosides, 

 "protagon" and various carbohydrates. Page's later study of the 

 fats and lipoids of the echinoderm egg led to the conclusion that 

 (qualitatively) there was more kephalin in the eggs of Arbacia than 



