222 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



camera drawings, with a Bausch and Lomb one-eighth objective, and 

 are reduced one-half in photolithography. The stolon exhibited no 

 traces of constrictions, although Fig. 9 is from the tip of a stolon a little 

 older, with faint indications of two or three constrictions at its tip. In 

 Fig. 4, from the root of the stolon, the greater part of the germinal mass 

 consists of embryonic cells like those shown in Plate XLI, Fig. 7, 

 although the cells on the ha3mal side are arranged in a distinct epithelial 

 layer, which passes gradually at the sides into the undifferentiated mass 

 without any sharply defined limit. An orange color has been used for 

 the undifferentiated cells and blue for the epithelium, and the contrast 

 of these colors gives to the epithelium in the drawings a sharpness which 

 is unnatural. In Fig. 5 the epithelium has almost, and in Figs. 6, 7 and 

 8 it has quite surrounded the central cells, which, from this time on, are 

 conspicuously different from those of the epithelium. The nucleus is 

 much larger, and it has a large, conspicuous nucleolus, which is suspended 

 near the center of the nucleus by a network of fine threads, which all 

 unite again in a granular layer around the periphery of the nucleus. 

 These structures all stain intensely, while the remainder of the nucleus 

 remains clear and colorless, without any traces of the staining fluid. The 

 nuclei are imbedded in a granular yolk, in which the cell boundaries are 

 unrecognizable, although they were faintly indicated at the stage shown 

 in Fig. 5 and in Plate XLI, Fig. 7. As we pass from the base of the 

 stolon to the tip, Figs. 5, 6, 7 and 8, the yolk grows more and more 

 abundant, the nuclei grow larger, and the threads of chromatin become 

 larger and more numerous, the nucleolus especially increasing in size 

 and in the definiteness of its outline. Plate XXXIV, Fig. 4, is a longi- 

 tudinal section, or a section at right angles to Plate XXXI, Fig. 8, in 

 nearly the same part of the germinal mass, although the latter figure is 

 from the tip of a young stolon, while Plate XXXIV is from the base or 

 root of an old one. At about the stage of development shown in these 

 figures, the outlines of the eggs become much more distinct than they 

 were at earlier stages, and the eggs have now attained to nearly or quite 

 their full size. It is important to note that this condition is reached both 

 in the young stolon, Plate XXXI, Fig. 8, and also at the young end of the 

 mature stolon, before any traces appear of the bodies of the chain-salp*. 

 At the stage of Plate XXXIV, Fig. 1, the stolon is a continuous tube, but 

 at the stage of Figs. 4, 5 and 6 we find the nerve-tube t, the perithoracic 

 tubes w, and the digestive tube d', continuous, while the bodies of the 

 salpa3 are indicated only by the undulating outline of the ectoderm, Figs. 



