PLATE 3 
EXPLANATION OF FIGURES 
24 to 27. Cleavage aspects of Tubularia crocea. (Reproduced from drawings 
made by G. T. Hargitt illustrating his paper on early development of Pennaria 
tiarella and Tubularia crocea. Bull. Mus. Comp. Zodl., vol. 53, no. 3, by per- 
mission. ) ; 
24 Cleavage planes which are complete, are more or less vertical, but the equa- 
torial furrows are shown in several of the blastomeres. 
25 to 26 Two sections of anegg showing extremely elongated and erratic 
aspects. The several spaces shown are designated as cleavage cavities. This 
view I have taken occasion to question in the text of the present paper. 
27 So-called blastula stage. This point I have also shown to be a mistaken 
view. In fact it may be questioned if in any case the term blastula should be 
applied to early stages of cleavage such as this. 
28 Section of an egg of Pennaria tiarella in early cleavage. This is an egg 
which has shown an unusual regularity in cleavage behavior. WN shows a typical 
resting nucleus, of which several others are shown. At N’ is shown a nucleus in 
what seems amitotic cleavage. In this egg are seen also several inner spaces, but 
which are extremely transient phases. 
29 Morula of Clava. The pro-entoderm has been tinted to show the early 
physiological differentiation of these cells. A discussion of this may be found 
in the text. 
30 Morula of Hybocodon prolifer. As compared with preceding figures of 
Tubularia, Pennaria, e¢ al., it shows the same indefinite intercellular spaces, but 
no distinctive blastocoel. Several nuclei here shown resemble much those of 
Clava, and appear in some cases in amitotic division. 
31 Nucleus of Clava just prior to maturation. Thenucleolus is conspicuously 
vacuolated. Chromatin is in process of fragmentation and dispersal. Stained 
by picro-hematoxylin which differentiates the yolk beyond mistake, and makes 
certain the chromatin nature of these granules. X 800. 
32 Nucleus of Clava in process of fragmentation and dissolution. First polar 
body already discharged. Nucleolus in process of collapse; chromatin fragmenta- 
tion well advanced. Stain as in previous egg. > 800. 
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