294 THE PHYSIOLOGY OF REPRODUCTION 



but some of the protein material undergoes partial oxidation, to 

 uric acid, and may thus contribute to the " energy of development." 

 Whether the glycogen which disappears during development serves 

 as a source of energy is doubtful. The chitin which is deposited in 

 the cuticle of insects is a compound built up mainly of carbohydrate- 

 groups, and it seems likely that these carbohydrate-groups are derived 

 from the glycogen, which thus contributes to the formation of the 

 cuticle. It is interesting to note that glycogen appears to fulfil a 

 similar function in the developing rabbit, where it also contri- 

 butes to the building up of the growing tissues. 1 It appears 

 indeed to be a general law that carbohydrate material is essential 

 for growth. 



Another point which emerges from these considerations of 

 comparative biochemistry is that the synthetic capacity of the 

 developing ovum remains constant throughout the different classes 

 of animals which have so far been investigated. Thus in every case 

 investigated the developing ovum has the power of synthesising the 

 purine bases, while conversely it is unable to synthesise cholesterin, 

 or at any rate does not require to do so, since cholesterin is always 

 present in the egg, in amounts equal to or greater than those found 

 in the developed embryo. Only one exception to this rule has so 

 far been observed : in the starfish egg cholesterin is absent. 2 



The pigments have been studied especially in the eggs of Crustacea. 

 From the eggs of Maja squinado, Maly 3 isolated two pigments 

 a red pigment, Vitellorubin, which is extremely sensitive to light, 

 and a yellow pigment, Vitellolutein. These pigments belong to 

 the lipochromes or luteins, which have been mentioned above. 

 Krukenberg 4 has examined the pigments of a number of other 

 Invertebrates. All these lipochromes have characteristic absorption 

 spectra. 



The lipochromes of Maja are of special interest, because a similar 

 pigment, Tetronerythrin, has been found in the blood of Maja and 

 other Crustacea. The amount present in the blood shows consider- 

 able variation. According to Heim 5 it is completely absent in the 

 blood of the male, and appears in the blood of the female during 

 ovulation. At this period also the ovaries, which usually have' a 

 yellowish or whitish colour, become first bright yellow and then red. 



1 Lochhead and Cramer, loc. tit. 



2 Mathews, "An important Chemical Difference between the Eggs of the 

 Sea-Urchin and those of the Starfish," Jour. Biol. Chem., vol. xiv., 1913. 



3 Maly, "Uber die Dotterpigmente," Berichte der Akademie der M7,w?z- 

 schaften, in Wien, vol. Ixxxiii., 1881. 



* Krukenberg, Vergleichende physiologische Studien, II. Eeihe, 3 Abteilung, 

 1882, p. 6. 



5 Heim, " Sur les Pigments des CEufs des Crustaces," Compt. Rend. Soc. BioL, 

 vol. xliv., 1892, p. 467. 



