No. I.] MESENCHYME IN CERTAIN LARVAE. 



17 



that of the other, which serve to bind the cells firmly together. 

 The other branches are at first of about the same size, but one 

 branch from each cell, extending outward {i.e., away from the 

 twin cell), becomes very quickly larger than the rest, sometimes 

 approaching the diameter of the cell itself. These two larger 

 branches are seldom in the same straight line, but usually 

 make a more or less 

 obtuse angle with 

 each other. That they 

 are really branches 

 and not simply a pro- 

 longation of the cell 

 body is apparent from 

 the fact that they are 

 finely fibrous in struc- 

 ture like all the other 

 branches, and not 

 granular like the body 

 of the cell. 

 These large branches 

 extend some distance from the cell and then divide dichoto- 

 mously, ending in fine fibrils. 



The smaller divisions of these branches, together with those 

 of the cell itself, anastomose freely and form a loose reticular 

 network. These details of structure appear to better advantage 

 in the enlarged drawing of the two cells shown in Fig. 2. 



At this stage of their development they are not attached to 

 anything except to each other, but the network formed by their 

 interlacing branches extends over a considerable area and holds 

 them in position. 



They appear like ordinary mesenchyme cells, but upon being 

 watched they are seen to possess a peculiar contractile power, 

 which is manifested at intervals. In a few individuals the con- 

 tractions occurred at definite intervals as long as the cell was 

 watched, but more frequently there was a period of rest after 

 a few contractions. Both the time of contracting and the 

 intervals of rest were subject to considerable variation, but the 

 latter was never long enough to enable a camera lucida sketch 



Fig. 2.— The two contractile cells enlarged to show their 

 structure. Cells relaxed. Cam. luc. drawing, Leitz ob- 

 jective No. 7, Eye-piece No. 3. 



