io6 Papers from the Marine Biological Laboratory at Tortugas. 



f erred to fresh sea-water. In the best cultures the number of agglutinations 

 and subsequent fusions were as numerous as in the best cultures of Arhacia 

 with the modified Driesch's method. 



EARLY DEVELOPMENT. 



Inasmuch as I have elsewhere described in detail the early develop- 

 mental changes in agglutinated and fused embryos of Arhacia and since the 

 changes in Toxopneustes are essentially identical with those in Arbacia, I 

 will only supplement the previous account by stating briefly at what stage 

 and under what circumstances agglutination occurred after treatment with 

 the NaCl solutions. 



The addition of an isotonic NaCl solution to sea-water involves a dilution 

 of the other sea salts and a concentration of the NaCl. The excess NaCl 

 stimulates the eggs to develop more rapidly, provided that the solution does 

 not contain more than 50 per cent of the NaCl solution. In solutions con- 

 taining 50 to 60 per cent NaCl solution, the excess NaCl seems to be neutral, 

 but beyond this quantity with 90 or more per cent development was dis- 

 tinctly retarded and atypic. That the eggs in the NaCl solutions absorbed 

 water was evidenced by the distinct increase in size over the corresponding 

 controls, and by the diminution in the space between the egg and the fer- 

 tilization membrane. In many instances the fertilization membrane burst 

 and a part of the protoplasm of one or more of the blastomeres protruded 

 from the fertilization membrane, while in other eggs this membrane was 

 completely thrown off. 



The differential rate of development in the NaCl solutions closely paral- 

 leled the differential rate of regeneration in varying concentrations of sea- 

 water. This suggested that the agglutinations might be due to a graded 

 intake of water. But no agglutinations occurred in ordinary diluted or 

 concentrated sea-water, or in sea-water to which MgSo4, K, Ca, or Li salts 

 had been added, or in sea-water to which various anesthetics had been added, 

 or with eggs whose fertilization membranes had been removed, or in sea- 

 water rendered alkaline. The NaCl in the above experiments must have 

 affected the eggs in such a manner as to gelatinize their outer surfaces, and 

 under these circumstances, when two or more eggs whose fertilization mem- 

 branes were ruptured came in contact, they were agglutinated. Some of 

 these agglutinated eggs subsequently separated, others remained aggluti- 

 nated, developing into more or less perfect twins, while others fused together. 

 I have never observed fusion during the egg stage, as reported by Haan. The 

 fusion in both Arbacia and Toxopneustes occurred and was limited to the 

 blastula and gastrula stages, as described in a previous publication. In 

 these studies and in those of other workers in this field attention has been 

 chiefly directed to the fusion of the ectodermal walls of the two embryos 

 and to the fusion of their archentera. The skeleton seems to have been 

 overlooked. Curiously enough the changes in the skeletons of two fusing 

 larvae Indicate most clearly the nature of the regulatory phenomena during 



