10 BULLETIN OF THE 



a longitudinal section of a portion of the body wall passing through the 

 non-budding region. The wall seems to consist of one layer only of cells, 

 and a fine, non-stainable cuticula. This layer of ceils is the ectoderm, 

 for it can be traced directly into the outer layer of the tip. The meso- 

 dermal layer is not represented in the region from which the figure 

 was drawn, but I believe it is not entirely absent from this part of the 

 individual, for occasionally extremely flattened cells, spindle-shaped in 

 section, may be seen lying inside of the ectodermal layer, quite sharply 

 marked off from it by a distinct line. Further evidence of the existence 

 of two layers is found in the fact that one occasionally sees in the flat- 

 tened body wall two nuclei lying together, one nearer the coelom than 

 the other. The cells of the ectoderm are seen to be very much flattened 

 (average 2.5 fi), and their nuclei are widely separated (35 fx). The nuclei 

 ai'e oval, and rather smaller than those near the tip. They possess a 

 single, rather large nucleolus, which does not stain intensely. The cell 

 protoplasm stains very little. The cuticula is about 0.5 jx thick. 



If we study the body wall in the budding region, when the latter is 

 first indicated on the surface by a marked protrusion of the outline of 

 the zooecium (Plate II. Fig. 15), we find that this protrusion is due to 

 an elongation of cells. There are about twenty-two cells in this section, 

 which are more or less thickened. Since the section figured passes 

 through the centre of the circiilar thickening, and is about one sixteenth 

 the diameter of the circle in thickness, it follows that there are over 250 

 cells of the ectoderm which have already at this stage become somewhat 

 enlarged previous to evagination. The highest of these cells are the 

 central ones, of which the largest is 22 fi high. The largest nuclei are 

 4/iby 6.3 fi, which approximates the size of those in the gemmiparous 

 region (page 6). They are placed nearer the coelomic epithelium than 

 the exterior, are nearly spherical, and each possesses one large nucleolus 

 and a quite apparent network with deeply stainable nodal points. The 

 cell body is stained as a whole rather deeply by Ehrlich's hsematoxylin, 

 but particularly around the nuclei. The outer parts of the central cells, 

 however, are stained very little, and the deep ends of some of the lateral 

 cuboid cells not at all. The network of plasma contains only fine 

 granules, and these seem to lie in rows parallel to the long axis of the 

 cell. The structure of the outer-layer cells, at a somewhat earlier stage, 

 is shown in Figure 18, under a higher magnification. The network is 

 very apparent in these large spherical nuclei, and the plasma of the cell 

 is seen to contain coarse granules, which lie near the nuclei and stain 

 deeply. 



