DR. E. B. WILSON ON THE DEVELOPMENT OF RENILLA. 753 
points out the fact that intra-cellular or amceboid digestion is confined, so far as known, 
to the most primitive groups of the Metazoa and in the Cceetenterates seems to be 
the normal and most frequent if not the only process. The digestive functions of an 
entoderm cell in these cases are identical with those of a unicellular Protozoa, and 
MEtscuNIkoFF is inclined to consider the former as an actual survival of the latter—a 
physiological character which was originally present in all Metazoa then existing, and 
has only been lost in higher forms. LANKESTER even suggests that the absorption of 
unsaponified fats in the highest Metazoa may possibly be a last relic of the primitive 
mode of digestion. 
None of the writers on this subject have pointed out the identity of the process with 
that of the absorption of the yolk in Astacus, described by RetcHENBACH in 1877 
(Zeitschrift fiir Wiss. Zool., Bd, xxix., 1877). In this case the amoeba-like action of 
the entoderm cells was observed with the greatest clearness. The cells put forth large 
pseudopodia, and actively engulph the yolk-granules which were observed in every 
stage of the passage from the yolk-mass into the cell-bodies. The ingestion takes 
place, it is true, at the basal instead of the apical end of the cells, since the yolk lies 
outside the archenteron ; but this circumstance does not tell against the identity of 
the process with that of adult Coelenterata and Turbellaria and of the larval Renilla. 
Wo trson has observed a similar process in the yolk-absorption of Lymneus, and in this 
case the nutriment, as in Renilla, is contained within the archenteron (see Bulletin de 
lAcadémie Impériale des Sciences de Saint-Pétersbourg, tom. xxvi., pp. 79-99, 1880. 
Lu le 9 Octobre, 1879). 
It is interesting to find the embryonic entoderm cells exhibiting this primitive 
mode of digestion, though it is clearly to be regarded simply as an adaptation connected 
with the presence of a large amount of food-yolk. Still the idea is suggested that the 
ameeba-like ingestion of food in the larva may perhaps be due to a kind of reversion, 
the reappearance in the larva of a feature which, in the case of Astacus and Lymneus 
at least, has become quite dormant in the adult. Whether it exists in the adult 
Renilla I have been unable to determine, but it cannot be observed in the young 
transparent colonies (see p. 786), 
Whatever be the mode of absorption, the granular basal zone, so often referred to, 
appears to be a reserve store of food-material—either the actual remains of the ingested 
food-granules, or a new store of granules laid up for future use by the protoplasm after 
being richly fed. It would seem that the cell packs away its reserve supply of food in 
its basal part, leaving the apical or inner end free to continue the active work of 
feeding ; so that there is in a sense a physiological division of labour within the cell, 
It is noteworthy that the entoderm nucleus is invariably situated in the inner part of 
the cell which contains the coarser granules. This position of the entoderm nuclei 
appears to be not uncommon in embryos where the gastric cavity is filled with food 
material (compare Lumbricus, t. KLEINENBERG, and Planorbis, t, Rasu) ; and Rast has 
