Experimental Studies on Germinal Localization. 229 



basals; but in every case the embryos became abnormal or died 

 without division. I therefore resorted to the method of allow- 

 ing the eggs to continue their development for 24 hours in the 

 calcium-free water, separating the cells from time to time by 

 directing a rather strong jet of water upon them by means 

 of a fine pipette. In this way the cells may be almost com- 

 pletely separated so as to produce what is in effect a pro- 

 gressive maceration of the larva without killing the cells. The 

 result is most striking. At the end of 24 hours the whole em- 

 bryo is disintegrated into its constituent cells, some of them lying 

 in small groups, but in favorable cases many are completely iso- 

 lated. The greater number of these cells are motionless and 

 perfectly spherical, of many different sizes, and still appear to be 

 living and in a healthy condition. Among these are swimming 

 with great vigor numbers of trochoblasts, singly, in pairs, or 

 sometimes in groups of four or three (Figs. 49-55). Measure- 

 ments of these trochoblasts show that in Patella they are of two 

 sizes, in Dentaliinn, as pointed out above, of three, the larger one 

 agreeing perfectly with the primary trochoblasts obtained by in- 

 dividual isolation, the smaller with the secondary trochoblasts. 

 Here and there can sometimes be seen a single apical cell, with 

 its chai'acteristic radiating sensory hairs. 



Among the motionless rounded cells it is impossible to dis- 

 tinguish the different categories by their structure, since all have 

 the same form and all are filled with yolk spheres. In view of 

 the foregoing results, however, it can hardly be doubted that the 

 largest ones are isolated entoblast-cells. But the most interest- 

 ing cells are those which are not rounded but of a different form. 

 Two kinds of such cells can be distinguished, both in Patella and 

 in Dentaliinn, namely, spindle-shaped cells (Fig. 57), and branch- 

 ing mesenchyme-like cells (Fig. 56). The cells of both forms, 

 are relatively small, less heavily laden with yolk, and more trans- 

 parent than the others. /;/ all these respects these cells are closely 

 similar to the mesoblast-cells, as seen in total preparations or sec- 

 tions of the normal trochophore of the same age. 



These facts must be interpreted with considerable reserve; for 

 it is well known that isolated cleavage-cells often become irregu- 



