264 H. E. JORDAN 



young and actively growing bodies, and present in dividing cells, 

 they cannot be regarded as products of degeneration. Since they 

 appear to be true melanic granules they cannot be interpreted as 

 secretory in the stricter sense of the word. They make their 

 appearance as such first in the cytoplasm, under nuclear influence 

 probabl}'-, but apparently not as nuclear extrusions. In the pin- 

 eal body of the embryo sheep they appear only in small quanti- 

 ties in only very few cells; at half term they are more or less 

 abundant in almost all the cells. They are interpreted as mel- 

 anic mainly on morphological and optical grounds, and on the 

 basis of negative microchemical tests; i.e., they do not turn blue 

 in a 2 per cent acidulated potassium ferricyanide solution, hence 

 not haemosiderin, nor iron-containing; nor red in Sudan III, 

 hence not predominantly lipoid in nature. 



These granules must accordingly be regarded as most probably 

 melanic. What then is their significance? I must again empha- 

 size the fact that their decrease in later stages is probably only 

 apparent and not real. There are relatively fewer granules per 

 cell in consequence of a mechanical distribution, by mitosis, among 

 the more or less numerous descendants of the original pigmented 

 cells. The quantity of pigment in the final descendants thus 

 depends upon the endowment of the original ancestor, and the 

 number of intervening generations. Possibly small additions are 

 made in occasional generations and the large mass of pigment 

 granules in old glands seem due to local unusual (primitive?) 

 conditions stimulating to excessive pigment production. Re- 

 garding the significance of this voluminous" pigment production 

 among the parenchymal cells of the foetal pineal body, two more 

 reasonable interpretations suggest themselves. The one must be 

 expressed in terms of the biogenetic law; the other in terms of 

 nutrition. The second assumes that melanin is chemically pro- 

 teid plus lipoid in varying proportions and capable of transforma- 

 tion into usable food material. But it appears the less valid since 

 the granules do not increase concomitantly with growth, nor ever 

 wholly disappear. Assuming that the mammalian pineal body 

 represents the epiphysis of reptiles, or other progenitors in the 

 direct mammalian ancestry, where it functioned as a visual or 



