752 
DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 
the yolk is completely absorbed the contents of the entoderm cells again change 
their character, as shown in fig. 130 (fifty-two hours). They become once more clear, 
and the basal granulation nearly disappears. The cells still contain a considerable 
quantity of granules, but the contrast with the preceding stages is marked. The 
cell-outlines consequently become much more distinct. The nuclei are deeply stained, 
very conspicuous, and are situated always in the inner parts of the cells. 
Conclusions. 
Although I have made many sections of larvae prepared by various methods while 
yolk-absorption was in progress, I have failed to obtain decisive evidence as to the precise 
modus operandi by which the yolk-cells or their remains are absorbed by the entoderm 
cells. This failure is due to the excessive minuteness and delicacy of the tissues 
which renders it extremely difficult to make satisfactory preparations of them. But a 
careful study of the sections inclines me to the belief that the smaller particles of the 
yolk-debris are engulphed bodily by the entoderm cells Amoeba-fashion, the process of 
digestion being completed within the body of the cell : that, in other words, the young 
Renillci is nourished by a form of intra-cellular digestion. As we have seen, the cells 
are at first clear and nearly destitute of granules. They become granular, however, 
and increase in size as soon as the disintegration of the yolk-cells begins, and their 
granular appearance continues until the absorption of the yolk is completed, when 
they become again clearer. The large, coarse granules in their inner ends (i.e., those 
turned towards the yolk-mass) have the same appearance as the small yolk-granules 
lying just outside the cells, and the entoderm often contain rounded granular masses 
which are very similar, though with less distinct outlines, to the yolk-spheroids of the 
digestive cavity. The spheroids may often be observed to lie directly upon the ento¬ 
derm cells, and the inner ends of the latter are sometimes produced into small 
amoeboid processes reaching out into the digestive cavity, though this is rare. 
These appearances suggest, though they do not prove, that the yolk-granules and 
spheroids pass bodily into the cells. I have never seen them in the act of passing 
into the cells, but the technical difficulties are great, and the other considerations 
seem of sufficient weight to warrant the provisional acceptance of the view advanced 
above. 
This conclusion, if well-founded, is of interest in connexion with recent discoveries in 
regard to intra-cellular digestion in Coelenterata and Turbellaria. The occurrence of 
such a form of digestion in the sponges has long been a familiar fact, and the more recent 
researches of Metschnikoff, Claus, Gegenbaur, Parker and Play Lankester have 
shown that an essentially similar mode of digestion occurs in the adults of many 
Coelenterata belonging to the higher groups, namely : in Hydra, Hydroid polyps, 
Hydromedusae, Acalephs, Actiniae, Ctenophora and Siphonophora. Metschnikoff 
showed in 1878 that the same remarkable process takes place in a number of fresh 
water Turbellaria, and he has ascribed to it an important phylogenetic significance. He 
