MUSEUM OF COMPARATIVE ZOOLOGY. 7 



staining plasma ; the inner ends of the cells, however, do not stain so 

 deeply as the middle or peripheral portions. 



The cuticula (omitted from Fig. 3, see Fig. 5) is usually somewhat 

 different in appearance from that at the extreme tip. In section we can 

 distinguish two layers : an outer, thicker, deeply staining layer, which is 

 not continuous but appears broken into larger or smaller bits ; and an 

 inner, thin, non-stainable and highly refractive portion, from which the 

 first layer is often slightly separated. This second layer is closely applied 

 to the underlying cells, which doubtless secrete it. Looked at from the 

 surface (Fig. 10, a.) the deeply stainable layer is seen to be broken into 

 irregular polygonal pieces ranging from 2 ju to 17 /x in diameter and sepa- 

 rated from one another by spaces ranging from to 6 /x. 



The mesoderm forms a loose epithelium, whose average width is less 

 than that of the ectoderm (Fig. 3, ms'drm.). As a whole, moreover, it 

 stains less deeply. In a portion of the gemmiparous zone, which lies 

 about 180° from the budding region, the mesoderm has become so delicate 

 a layer, if it exists at all, as not to be easily distinguishable. In the vicin- 

 ity of the bud its cells have irregular outlines and extend out into the 

 coelom as though possessed of the power of amoeboid movement. The 

 nuclei are spherical or ovoid, smaller than those of the ectoderm, and on 

 the whole have smaller nucleoli. The cell body is highly vacuolated. 

 The vacuoles are not large and clear in outline, but whole regions of the 

 cell body seem to be reduced to a non-stainable condition, and in some of 

 these regions a fine network may still be observed. 



The proximal zone (Fig. 14, y to 8) is distinguished, soon after the 

 first rudiment of the bud appears, by the diminished thickness of the 

 ectoderm. The cells have become transformed from a columnar to a 

 pavement epithelium. The nuclei are smaller, the nucleoli less prom- 

 inent, and the cell body stains much less deeply. The cuticula is of 

 two kinds, as before, but with this difference : the deeply staining outer 

 part is less conspicuous, and the pieces are smaller and more widely sep- 

 arated. Looked at from the surface, we find an appearance like Figure 

 10, c, in which the dark bodies represent the deeply staining cuticula. 

 These pieces are much smaller than those of the gemmiparous zone, 

 ranging from 0.6 /n to 9.5 /x in diameter, and separated from each other 

 by spaces ranging from to 13 /*. 



3. Origin of the Polypidb in the Terminal Bud. 



Observation having shown that budding in Palndicella follows definite 

 laws, we ought to be able to discover the place and time at which buds 



