THE PRODUCTION OF GRAFTED EMBRYOS. 97 



Type b, pair of plutei with a common blastocoele, Fig. 90, 

 drawn from life at greater magnification. 



Type c, fusion of two, but with double set of organs, very few 

 examples, Figs. 94 and 82. 



Type d, fusion of two with partially double archentera, Figs. 

 73, 74 and 75. 



Type e, complete fusion with but a single set of organs, the 

 pluteus of Figs. 88 and 78. 



Type/, single body with a second parasitic archenteron, Figs. 

 84, 92 and 93. 



THE DEVELOPMENT OF INDIVIDUAL CLUSTERS. 



In an effort to follow the developmental and regulative proc- 

 esses, during agglutination and fusion, each cluster was isolated 

 and examined at periodic intervals. The very large groups 

 separated into their component members, as already pointed out, 

 each developing into a normal larva or the inner ones disinte- 

 grated bringing about the disintegration of the entire cluster. 

 The very small groups usually remained intact. Sketches and 

 memoranda made during the development of these small clusters 

 clearly showed that the types of agglutinated and fused eggs, 

 embryos and larvae described in the previous section, were not 

 the artificial results of preservation, but represented various 

 serial steps in the development and regulation of such clusters. 

 To describe these isolated groups would be to repeat the descrip- 

 tions of preserved material given in the preceding section. 



This statement applies with equal force to fused clusters, 

 though not all types were observed in the isolated clusters. The 

 following are some of the true fusions observed : 



Two eggs fused into a single body with two independent 

 archentera equal in size, Fig. 94, l or unequal, Fig. 93. 



Two eggs fused into one body with two archentera attached 

 end to end. 



Three eggs fused into one body with three independent 

 archentera. 



Two fused eggs and one egg fused to a blastomere developed 

 independent archentera, Fig. 95, which subsequently came in 

 contact and fused into one very long archenteron, Fig. 94. 



1 Figs. 93 to 95 are drawn from hand sketches. 



