98 George Lefevre 



sperm or treatment with the solutions. The unfertiHzed control 

 eggs, however, for the most part retain the compressed form w^hen 

 allowed to remain in normal sea-water, and finally die in this con- 

 dition. The eggs, furthermore, when taken from the tubes, are 

 naked, and the failure of the control eggs to ever form a membrane 

 furnishes an additional check on the experiments, for, as will be 

 shown beyond, every egg subjected to the action of the acid solu- 

 tions throws off a fertilization membrane in all respects identical 

 with the membrane which appears upon the entrance of the sperma- 

 tozoon. 



For the study of sections, eggs and embryos were killed in 

 Wilson's picro-acetic mixture (2 per cent acetic) which gave ex- 

 cellent results. Osmic acid (i per cent), followed by prolonged 

 immersion in Miiller's fluid, proved very satisfactory for later 

 stages, while weak formalin and a mixture of 2^ per cent formalin 

 and 50 per cent alcohol were useful for the demonstration of cilia 

 in total mounts of the older embryos and larvae. Sections were 

 stained in iron haematoxylin, with or without a counter stain, 

 while Conklin's Delafield's haematoxylin gave the best results 

 for whole preparations of the cleavage stages. Most of the sec- 

 tions were cut ^n in thickness, and all of the drawings were made 

 with the camera. 



IV EXPERIMENTAL RESULTS 



At the beginning of the investigation, the attempt was made 

 to induce parthenogenetic development by the use of salts, and 

 MgClj, Ca(N03)2, KCl, and NaCl were tried. All, however, gave 

 negative results, except in a few cases an irregular fragmentation 

 of some of the eggs was produced, but it never led to the formation 

 of swimming larvae. In many of these experiments the osmotic 

 pressure of the sea-water was increased, and it would seem, there- 

 fore, that parthenogenetic development of Thalassema cannot 

 be produced by subjecting the unfertilized eggs to the action of 

 hypertonic sea-water. It should be stated, however, that the 

 range of salt solutions employed was not exhaustive, since early 

 in the work it was found that acids gave promise of better results, 



