156 



enlargement of their nuclei may very well be corapared with the 

 sitnilar increase of size of the nutritive tnacronucleus of the Ciliata 

 and of the nuclei found in the yolk syncytia o/ Elasinobranchs 

 and Teleostei, the function of which is to control the liquefact- 

 ion and elaboration of the yolk l ). In this connection it is not 

 without significance that in certain abnormal cases — in the tro- 

 phoblast of an embryo which appeared to have died, and in the 

 trophoblastic débris found in the iuterplaceutal extravasations 

 already mentioned — brown iron-containiug granules were found 

 which appear to be due here, as they are stated to be due in 

 certain pathological conditions where they are well kuown, (in 

 pulnionary apoplexy for example, and in brown induration of the 

 lung) to the degeneration of the blood corpuscles which the meg- 

 alokaryocytes, have ingested. I have also succeeded (though 1 do 

 not wish to lay too much stress upon the fact because of the 

 considerable difEculty of conductiug the iuvestigation without 

 introducing some iron compound during the process), I have also 

 succeeded in demonstrating the presence of a masked (to use 

 Macallum's expression) iron compound in the normal megalokaryo- 

 cytes. I have interpreted these facts as meaning that when, for 

 whatever reason, the megalokaryocytes are unable to get rid of 

 the iron compound which they have obtained by the digestion of 

 the maternal corpuscles and which ordinarily they pass on to the 

 embryo, this compound remaining in the cells, becomes decom- 

 posed into the brown gianules of inorganic or albuminate of iron. 



During this period the embryo is probably also nourished by 

 the sugar derived from the glycogen in the maternal glycogen cells. 



In the third period the area vasculosa of the yolk-sac and the 

 allantoic circulation are both well established. 



In the yolk-sac the cells of the richly folded columnar epithe- 

 lium absorb the fat secreted by the glauds of the inter-placental 



1) An interesting parallel to the conversion of originally small and flat trophoblastic 

 cells into megalokaryocytes is seen in the formation of 'macrophages' from cells of the 

 peritoneal epithelium; see Durham : The Mechanism of Reaction to Peritoneal Infection: 

 Journ. of Path. and Bact. Vol. IV, 1897. 



