356 THEOPHILUS S. PAINTER 



to America. I take this occasion to express my thanks to 

 Professor Boveri for suggesting the problem and for placing the 

 necessary material at my disposal. 



In preserving the eggs, a mixture of 4 parts 95 per cent alcohol 

 and 1 part glacial acetic acid was used. They were stained 

 in toto and mounted in glycerine. 



DESCRIPTIVE 



Among the embryos which had been allowed to undergo full 

 development, one finds perfectly normal specimens; specimens 

 in which only one end of the body is developed; and lastly, 

 totally disorganized embryos. The problem was primarily 

 to determine the causes which produced the abnormalities 

 observed, but as the work went forward a number of other 

 questions of general interest came up which will be touched upon 

 m the following paper. ^ 



A drawing of a normal worm, which developed from an egg 

 exposed for three months to carbon dioxide, is given in figure A. 

 A blunt anterior end with the pharynx and the pointed posterior 

 end may be seen, and, in addition, towards the posterior part of 

 the body the large deeply-staining nuclei of the primordial 

 germ cells. Typically there are only two of the latter but 

 occasionally more occur; in one case six were present. 



The abnormal embryos are of two general types. One of these 

 has the posterior end of the body fully developed while the 

 anterior end is disorganized. The second type is characterized 

 by the absence of organization in its blastomeres. The first 

 type of embryos is shown in figure B. This occurs in roughly 

 33 per cent of the embryos (in 54 cases out of 165 examined for 

 the point). The pointed posterior end is clearly seen together 

 with the primordial germ cells, but there is much variation in the 

 degree to which the posterior part of the body is developed. We 



s A brief description of the normal development of Ascaris is given on page 367. 

 Any one not familiar with the cleavage, or with the nomenclature, in this worm, 

 will find it helpful to read this over together with a glance at the schematic dia- 

 grams given. The nomenclature of Boveri has been used throughout the present 

 work. 



