348 THE UNFERTILISED EGG AS A [pt. iii 



of the membrane proteins in the centrifugal layer caused this 

 effect. 



It is of course a fact of the first importance that normal develop- 

 ment can follow centrifugation and this will receive attention later 

 (see Section 3 and the Epilegomena) . I shall only mention here 

 as one of the best instances of this phenomenon, the work of 

 Schaxel on the axolotl egg. Here centrifugation caused atypical 

 discoidal cleavage which nevertheless resulted in a normally pro- 

 portioned embryo. Thus normal conclusions can follow abnormal 

 distribution of the so-called "organ-forming substances". For further 

 details of these experiments, see Morgan and Bertalanffy. 



The early work of Gobley on the fat of the hen's and the carp's 

 egg has already been described. He isolated glycerophosphoric acid 

 from the latter, and pursued further his investigation of lecithin, 

 concerning which it is of interest to note that Sacc contested his claim 

 to have found organic alcohol-soluble phosphorus. Sacc believed 

 that the fats contained dissolved in them a quantity of inorganic 

 phosphorus. Gobley, however, was easily able to disprove this view 

 and to show the identity of carp's egg lecithin with brain lecithin. 

 Data which have accumulated since Gobley's time on the fatty 

 substances of the eggs of the lower animals are collected in Table 44, 

 and may be compared with those in Table 22. One of the most 

 striking differences between the hen's egg and other eggs is the 

 relatively low iodine value of the fatty acids of the former, both free 

 and combined in lipoids. The neutral fat of the hen's egg has an 

 iodine value varying roughly between 60 and 90, but for fish eggs 

 the figures vary from 90 to 150, and the same rule holds generally 

 of the lipoid fatty acids, for they average 60 in hen and 100 in 

 fish eggs. The saponification numbers, on the other hand, are much 

 the same throughout the two tables (from 170 to 200). The conclusion 

 might therefore be drawn that egg fats differ rather more as to the 

 number of unsaturated linkages in their acids, than as to the length 

 of their chains. Nevertheless, there are remarkable exceptions to 

 these generalities, the fatty acids of the echinoderm eggs, for example, 

 having enormous saponification and high Dyer numbers, and there- 

 fore presumably only very short chains of carbon atoms. Arbacia 

 is more remarkable in this than Asterias. Yet, though they are 

 exceptional in that respect, they have iodine numbers very like those 

 of fish-egg fats. Another point of interest is that the cholesterol/fatty 



