RIGELOW: NUCLEAR CYCLE OF GONIONEMUS MURRACHII. 289 



phenomena connected with fertilization. It is my hope in a future com- 

 munication to consider the subject of the maturation of the egg. 



The work has been carried on under the direction of Professor E. L. 

 Mark, to whom I am indebted for unfailing support and helpful criticism ; 

 and I also owe a debt of gratitude to the Museum of Comparative 

 Zoology for allowing me the use of a laboratory. My thanks are spe- 

 cially due to Dr. Henry F. Perkins, who put at my disposal his collec- 

 tion of the young stages of Gonionemus, as well as to Mr. George M. 

 Gray of Woods Hole, Mass., for his care in preparing the adult speci- 

 mens of Gonionemus. 



II. Materials and Methods. 



The adult specimens of Gonionemus were fixed in Flernming's stronger 

 fluid, which proved entirely satisfactory, giving a beautifully precise 

 fixation, without noticeable distortion or shrinkage of the nuclei. In a 

 few cases excessive blackening occurred with a corresponding difficulty 

 in staining, but this was easily remedied by bleaching, either with hydro- 

 gen peroxide or with chlorine, neither of which reagents showed any 

 harmful action. A series of specimens was also prepared with the 

 picric-osmic-acetic-platinic fluid of vom Rath, and, although the cytologic 

 fixation thus obtained was in general inferior, these preparations proved 

 very useful for the study of the achromatic spindle figures and of the 

 centrosomes. For the purpose of studying isolated spermatozoa a dozen 

 or more medusae were prepared according to the isolation method of 

 the Hertwigs ('78), the fixation being that of weak osmic acid. For 

 the sake of checking the other methods and for the study of the general 

 structure of the gonad, a number of specimens were preserved simply 

 in 70 per cent alcohol and others in 5 per cent formalin. Finally, I 

 should mention that the material received from Dr. Perkins, on which 

 the study of fertilization and cleavage was carried out, consisted chiefly 

 of entire eggs and of some few series of sections, fixed in part in a 

 corrosive-acetic mixture and in part in strong formalin. 



Of a considerable number of staining fluids which were tried by far 

 the most satisfactory for all general purposes was Heidenhain's iron 

 haematoxyliu, either alone, or followed by one of the coal-tar plasma 

 stains, orange G, acid fuchsin, Congo red, Bordeaux red, or eosin ; while 

 for a check on the iron haematoxylin method, which Boveri (: 00) has 

 shown to be so essential, Delafield's haematoxylin was employed. For 

 the stiuly of the metamorphosis of the spermatid, iron haematoxylin, 



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