472 EMBRYOLOGY OF THE TURTLE. Part III. 
it ceases to be independent. This feature of the life of the mesoblast, however, 
more properly belongs to another chapter, in which it will be shown, that the 
once free cell may finally be recognized as entering bodily, but not in its pres- 
ent entity, into the formation of the embryo. 
We now proceed to consider the origin of the crystalloid entoblasts, of which 
we have already so often spoken in connection with the mesoblast. 
Formation of the Entoblast.' In the same egg in which a mesoblast first appears, 
the entoblasts also begin to develop, but singly at first (PI. 8, fig. 25b, a, b, 25, d). 
Their number very rarely amounts to more than two or three in each mesoblast, 
(Pl. 8, fig. 23d, e, 7, 2 fig. 25, a,) until the egg is from one eighth to one sixth 
of an inch in diameter. Casting the eye over the field of the microscope, there 
may be seen here and there a few of the minuter cells, contaming mesoblasts, 
which are rendered more conspicuous by the presence of a dark dot in the cen- 
tre of each (Pl. 8, fig. 23b, a, 6, 23d, d, f, g; Pl. 9, fig. 3a, 6a, n, 0; py): this 
dot is the nascent entoblast. Unlike the faint looming up of the mesoblast, the 
entoblast, minute as it may be in its incipient state, shows itself clearly and well 
defined, and usually with an irregular angular outline. The central orientation of 
this body, and its fac-simile repetition, in the same focus of centripetal influence, 
have been noticed before as a remarkable and unusual feature in concentric cell 
development; and now we would, in this its proper place, follow more in detail 
the elaboration of the design involved in its peculiar mode of growth. 
Rarely is a single entoblast permitted to attain any considerable size alone; 
but, soon after the declaration of the first, two or three more appear in the field, 
(Pl. 8, fig. 23d, ¢, 7, &, G 25, a; Pl. 9, fig. 3a, -e, fig. 8a, D, fig. 6a, m,) and thus, 
forming a cluster, proceed together m adding to their bulk. Soon, in a little 
older egg, more are added to the cluster, (Pl. 9, fig. 6a, d, f, g, h, %, j,) and 
again still others, (a, e,) until their number is beyond estimation, and the meso- 
blast is surcharged with them to its very wall (4). By this time the mesoblast has 
usually exceeded in diameter the radius of the ectoblast (a, 6, e). In two meso- 
blasts of the same size, (a and #4, also ¢ and e, or y and /,) the entoblasts 
differ both in number and size; those in one being oftentimes equal in length to 
the diameter of their parent, (a, 7,) whilst those in another are mere grains in 
comparison. The feature that particularly characterizes the entoblasts, and is prev- 
alent from the beginning up to this period, is a sharp angularity, which at times 
gives a spiculate appearance to the clusters. 
1 The name entoblast may apply to that part of the eribing the formation of the individual dots, we shall 
cell which is commonly called nucleolus, whether it use it in the plural. We shall also have occasion to 
consists of a single dot, or is made up of a larger or use the name of mesoblast in the plural, to designate 
smaller number of such bodies. However, while des- the parts into which it divides. See Ch. 2, Sect. 4. 
