ii8o 



FAT METABOLISM 



[PT. Ill 



and size, reaching a maximum at the time when the external gills 

 are half covered over by the operculum, and afterwards falling away 

 again. By the time the tadpole has reached a length of 17 mm. no 

 fat droplets are to be found in the cells. She concluded that some of 

 the fatty acids absorbed from the yolk were utilised in the cells of 

 the tissues, but that most of them were eventually transferred to stock 

 the newly formed liver cells. 



Among the histochemical researches, one of the most interesting 

 is that of Abe, who began by the not very hopeful statement that 

 "the anuran yolk is a complicated lipoid-protein mixture containing 

 phosphoprotein and iron", but went on to show that the utilisation 

 of the substances in it could not be going on at a uniform rate, 

 because in the early stages eosin stains the yolk light red or pink, 

 later dark red, and finally deep violet-red. No direct physico- 

 chemical meaning can as yet be attached to this, but it gives a glimpse 

 of the unequal utilisation of the yolk constituents which we have been 

 discussing. 



11-4. Fat Metabolism of Selachian Eggs 



We can now consider the events which take place in the fish egg 

 with respect to fatty acids during its development, and we shall 

 begin with the ovoviviparous selachians. In these fishes pecuHar 

 relations seem to exist between the liver of the "pregnant" fish and 

 the embryos within their transparent envelopes in its uterus. Lo Bianco 

 was the first to notice that whenever embryos were present the size 

 of the liver was increased, and this observation was confirmed by 

 Polimanti, who gave the following figures : 



Table 171. 



No explanation for this was suggested by Polimanti. A subsequent 

 paper by Reach & Vidakovich went further into the matter, as far 

 as the Torpedo was concerned, and Table 1 72 summarises the results 

 they obtained. Their first set of data, taken from fishes caught in 

 April, gives the figures for just after fertilisation, when the large- 



