22 A. J. GOLDFARB. 



and for the sake of brevity only a few stages in the development 

 of each cluster will be shown, all drawn to the same scale except 

 where specifically mentioned to the contrary, and all drawn from 

 the living specimens with the camera lucida. 



SINGLE LARVAE, AXES OF THE Two GRAFTED MEMBERS 



UNKNOWN. 



Under this heading are included those clusters which developed 

 into single perfect larvae, and in which the axes at the beginning 

 were either unknown, or could not be definitely ascertained. 



Fig. i is a foreshortened view of a pair of blastulse, par- 

 tially fused together. The diameter of each component when 

 compared with the controls clearly shows that these are two 

 blastulse and not two half blastulse. The axis of each member 

 could not be definitely ascertained until the blastopore, or better 

 still until the gut, is differentiated. Fourteen hours after the 

 stage shown in Fig. I the pair was transformed into a " single" 

 gastrula, with a "single" invagination shown in Fig. 2. This 

 gastrula developed into a "single" typical larva (Fig. 3), which 

 was essentially unchanged during the next four days. This 

 larva contained one skeleton and one gut, and if its history had 

 been unknown might readily be mistaken for a true single larva 

 derived from a single egg. 



Fig. 4 is another double blastula which developed into a 

 "single" large gastrula, and then into a young pluteus containing 

 a single pair of skeletal spicules, and a single gut (Fig. 5). Three 

 days after fertilization, it developed into what appears to be a 

 single perfect larva, shown in end view (Fig. 6). During the 

 next four days there was no essential change except the elongation 

 of the anal arms seen in Fig. 7 from a different view. 



Four stages are shown in the development of the next specimen. 

 Fig. 8 shows the giant blastula somewhat foreshortened. Fig. 9 

 drawn seven hours later, shows the giant gastrula with its single 

 gut a little to one side; fourteen hours later the gut is more 

 sharply to one side (Fig. 10). This gastrula developed into a 

 "single" short and somewhat atypic pluteus, containing a single 

 gut, still a little to one side, and a single asymmetrical skeleton 

 with one side distinctly enlarged (Fig. n). 



