312 A. RICHARDS. 



upon the work of Child and Hill and upon his own a priori con- 

 clusions. He offers nothing new on the problem. 



Direct division has been described in other cases of theoretical 

 importance but those mentioned above are perhaps the most 



significant. 



METHODS. 



My investigation on the problem of amitosis was suggested by 

 Dr. S. J. Holmes, to whom I owe much for direction during the 

 progress of the work. I have received numerous suggestions 

 from various other workers in the University of Wisconsin, all 

 of which are gratefully acknowledged. My thanks are also 

 due Drs. Grove and Meek, of the Pharmacology and Physiology 

 Departments, for their assistance in collecting material. 



Specimens of tape-worms were secured chiefly from dogs. A 

 considerable number of cats was examined, but only one fur- 

 nished material. The specimens were nearly all fixed in Flem- 

 ming's fluid, which proved quite satisfactory. Those taken from 

 the cat were fixed in Zenker's fluid to be used with Mallory's 

 connective-tissue stain. 



A variety of staining methods was used. Flemming's tricolor 

 stain did not give sufficient sharpness of detail to be of much 

 value. Iron haematoxylin is in general satisfactory, but it is to 

 be noted that the nuclei do not differentiate as readily as in many 

 other tissues. The fact that they do not decolorize readily and 

 often do not show their contents clearly must be borne in mind 

 when considering the significance of indentations of the nuclear 

 membrane. Delafield's haematoxylin decolorized in acid alcohol 

 gave excellent results. My greatest success, however, in stain- 

 ing this material has been by the use of Kernschwarz with 

 Lichtgriin as a counterstain. Lichtgriin is by far the best stain 

 for cytoplasmic structures that I have tried, its only drawback 

 being the ease with which it fades out. 



Two genera and three species of tape-worm have been used : 

 Tania marginata (Batsch), Tcenia serrata (Goeze), and Dypilid- 

 ium caninum (Leuckart). The last of these is the most favorable 

 for cytological work, but I have only a few specimens of that 

 genus. Even here the nuclei are quite small and not entirely 

 satisfactory owing to technical difficulties. I must protest against 



