Experimentally Fused Larva of Echinoderms, etc. 119 



variegatus. The skeleton under no circumstance fuses in the two individuals 

 and there is no evidence of an enlargement of the larva to form the "ein- 

 heits pluteus" or completely fused larva of Driesch. There is, on the 

 contrary, definite evidence that disintegration of skeletal materials takes 

 place in the suppressed larva without any corresponding enlargement of the 

 skeleton or the body of the dominant larva. The dominant larva in figures 12, 

 13, 14, and 15 are no larger than in figures 9, iob, 5, 6, 7B, and 8 — all 

 drawn to the same scale — or figures 11, iob, and 7A, drawn to greater 

 magnification. In the second place the dominant larva in these fusions are 

 no larger than the corresponding control larva, and the variation in size 

 is approximately the same in both groups. There are no giant larva in the 

 sense employed by Driesch and Morgan and other investigators. There 

 are completely fused larva as there are completely fused blastulse and 

 gastrulae. 



The facts clearly show that in the blastula, gastrula, and larval stages 

 the less or earlier differentiated tissues (such as ectoderm and entoderm) 

 after their union to form the giant body and giant gut diminish in size until 

 a normal single body and gut are approximated. This diminution must 

 occur either as a consequence of the degeneration of certain cells or the 

 diminution in size of the cells. The latter can readily be shown not to be 

 the case. 



It can also be shown that the degenerating substances in one larva do 

 not serve as food or stimulant of the other, for the dominant larva are no 

 larger nor do they develop any faster than the controls. In fact they are 

 considerably slower than the controls. 



The increased growth occurs not in any increase of the larval body 

 or of the contained organs, but in the hypertrophied and supernumerary 

 processes and bars whose origin and development have been described. 



SUMMARY. 



A new method was discovered by which large numbers of eggs of Toxop- 

 neustes variegatus could be fused together, during the blastula and gastrula 

 stages. The method consists essentially in placing the fertilized eggs in a 

 solution composed of one part of sea-water to three parts of either an 

 isotonic or a slightly hypotonic NaCl solution. 



This solution has two effects upon the eggs, namely, it increases the 

 volume of the egg and thereby bursts the fertilization membrane, and it 

 gelatinizes the surface of the egg. When any such eggs are in contact 

 they become agglutinated and may remain agglutinated and produce twin 

 larvae or fuse together during the blastula or gastrula stages. 



The conditions that favored the fusion process were: 

 (i) The number of agglutinated eggs: More than two eggs rarely gave rise 

 to a fused and characteristic larvae. When two eggs were agglu- 

 tinated they either developed into twin larvae or fused more or less 

 completely together. 



