CELL DIVISION IN T^NIA. 311 



regulatory growth. G. T. Hargitt was the first to suggest this 

 for hydroids. Child's work on Titbularia and Carymorpha sup- 

 ports this suggestion. In the growth and regulation of Planaria, 

 Bardeen and Child have reported amitosis. However, the figures 

 of Bardeen are far from conclusive, and it is very questionable 

 whether they justify the opinion that amitosis is the -method of 

 division here. Child has also worked on various other forms 

 among both vertebrates and invertebrates. In several of them 

 his evidence is lacking in some respects. Reference to his work 

 on the cestodes will be made later. 



A few workers have described amitosis in the cleavage of the 

 egg and in the early embryonic development of several forms. 

 Hargitt failed to find mitosis of the egg up to the sixteen-cell 

 stage, working on Clava leptostyla. Similar results obtain for 

 Eudendrium and Pennaria. Beckwith, however, has recently 

 shown that his results were due " simply to the fact that the eggs 

 were not obtained at the right time of day. In eggs collected at 

 the proper time (4 to 6 A. M.) there is no difficulty in proving 

 the typical stages of maturation and fertilization." " Maturation 

 and the early cleavages take place by mitosis and not by amito- 

 sis." Hickson and Hill have also studied ccelenterate eggs. 

 Hill in his account of Alcyonimn oogenesis shows that no polar 

 bodies are extruded, no chromosomes are present, the female pro- 

 nucleus divides irregularly by amitosis and then disappears, and 

 that probably the first cleavage nucleus is formed from the male 

 pronucleus. The evidence is not complete and the case should 

 certainly be reinvestigated. H. L. Osborne described cases of 

 amitosis in the food-ova of Fasciolaria. His results have been 

 corrected and enlarged upon by Glaser. The work of Glaser 

 seems to deserve the most careful consideration in regard to this 

 problem ; its bearing on the investigation herewith undertaken is 

 only general, however. Further work on embryos has been done 

 by Child, previously mentioned, and by Patterson on the pigeon's 

 egg. The observations of the latter, while much more extensive 

 than those of Child on the chick embryo, are in agreement with 

 them. Stoeckel thought binucleate ova in man are the result of 

 amitotic divisions. Pick's opinion on the subject of amitosis 

 as expressed in his survey of chromosome hypotheses is based 



