404 PROFESSOR LANRESTER. 



not yet assimilated — so in the corresponding phase of indi- 

 vidual development we find the food material consisting of 

 two kinds of granular matter, one of which has been taken in 

 by the egg-cell from its parent organism, assimilated and 

 deposited as the result of a chemical segregation, the other, 

 which is often of enormous relative bulk, consisting of coarse 

 granules or masses which have been engulphed by the pro- 

 toplasm of the egg during its sojourn in the maternal ovary 

 or ducts. Such coarse and bulky food material is prepared 

 for the young egg-cell by neighbouring cells of the maternal 

 organism, and may very fitly be compared, after it has been 

 incepted by the ovum, to the organic masses with which a 

 naked Protozoon gorges itself for purposes of nutrition. i 



The amount and the disposition of the food material iu the 

 ovum varies very greatly in different organisms. Its variation 

 is the direct cause of differences in the arrangement and size 

 of the cells into which the egg-cell divides, and becomes thus 

 the obvious source of discrepancy between the inferred an- 

 cestral (phylogenetic) and actual (ontogenetic) developmental 

 phases. 



The ancestral monoplast must have been free from any 

 large quantity of granular matter, whether segregated or in- 

 cepted, but we may assume its mode of taking food to have 

 been similar to that of the Amoeba, and that in response to 

 incidental and intrinsic forces its substance was differentiated 

 into an ectoplasm and an endoplasm. 



2. The polyplast=mulberry phase or morula (Haeckel). 

 — In the course of the historic development of animals, the 

 monoplast gave rise by division to spherical colonies consist- 

 ing of many adherent cells. These, we assume, continued 

 to nourish themselves by the inception of solid particles at 

 their free surface. The process which development appears 

 to have taken requires us to distinguish two conditions of 

 the Polyplast : a, an earlier one (Fig. 2), in which the con- 

 stitutional cells were closely adherent so as to form a solid 

 sphere, distinguished by Haeckel as the morula; b, a later 

 (Fig. 3), in which the accumulation of liquid at the centre of 

 the sphere built up by the cells gradually resulted in the for- 

 mation of a considerable cavity (the blastocoel, Huxley), so 

 that the polyplast now acquired the form of a vesicle, its wall 

 formed by a single series of equi-formal cells and its cavity 

 filled up by a liquid which had traversed the substance of these 

 cells. This hollow polyplast has been designated by Haeckel 

 the blastula. We must assume that food was still incepted 



' See my observations on the ovariau egg of Loligo, in the 'Phil. 

 Trans.,' 1875. 



