Febeuakt 25, 1916] 



SCIENCE 



265 



takes up the subject of the formation of the 

 polar bodies. In harmony with Buetschli's 

 discovery Schneider and ISTusbaum had de- 

 scribed the formation of the polar bodies in 

 Ascaris as a regular mitosis, whereas Van 

 Beneden and Carnoy insisted that it was a 

 different process. Boveri proved that the 

 former view is correct and was able to explain 

 many discrepancies of these authors by dis- 

 covering that there are two different varieties 

 of Ascaris in regard to their number of chro- 

 mosomes, called to-day univalens and bivalens. 

 It is of interest to note that he expresses here 

 the view that the recently discovered forma- 

 tion of a single polar body in parthenogenetic 

 eggs may be explained by the assumption of a 

 fertilization of the egg nucleus through the 

 second polar nucleus. In 1888 appeared 

 Boveri's Zellstudien II., dealing with the fer- 

 tilization and division of the Ascaris egg. 

 Here we find — besides many morphological de- 

 tails — ^his formulation of the theory of the 

 individuality of the chromosomes, founded, as 

 he freely recognized, by Eabl, and since one of 

 the fundamental principles of cytological re- 

 search. And he furnished important proofs 

 by comparing the prophases of the division 

 frith the last telophases, and further by show- 

 ing, that in cases of abnormal distribution of 

 tiie chromosomes as many of them came out 

 of the resting nucleus as had entered it. He 

 ■was further especially interested in the 

 mechanics of cell-division. He attributed a 

 great importance to the special plasm sur- 

 rounding the centrosome, the archoplasm (a 

 theory abandoned later by him), and pointed 

 to the importance of the continuity of the cen- 

 tral bodies called by him centrosomes, already 

 discovered by Van Beneden. And here we 

 find developed also his idea, that the main 

 importance of fertilization is the introduction 

 of a centrosome into the egg. Starting from 

 some abnormal cases, where a division of the 

 cell is possible without a nucleus, he reached 

 the conclusion that the centrosome is the 

 dividing-organ of the cell. It is of importance 

 to note that he emphasized even in this early 

 paper (pp. 10-11) the necessity of experi- 

 mental analysis of the phenomena of fertiliza- 



tion and heredity, recently inaugurated by the 

 brothers O. and E. Hertwig. 



To all these problems studied in Ascaris he 

 furnishes a supplement in Zellstudien IH., 

 1890, by applying the same studies on many 

 marine invertebrates during a sojourn at 

 ISTaples. For each of the objects investigated 

 he could prove Van Beneden's law concern- 

 ing the chromosomes in fertilization to be 

 correct. Further he shows that in all these 

 animals the reduced number of chromosomes 

 is found even at the beginning of the matura- 

 tion divisions in both sexes. The real reduc- 

 tion, therefore, must occur as early as in the 

 oogonia and spermatogonia. It may be added 

 here that diiring these years the complete 

 parallelism of the cycle of male and female 

 sex cells was definitely proven by the work of 

 Van Beneden et Julin, Boveri, Platner and O. 

 Hertwig, and that at the same time the prob- 

 lem of the reduction division was solved 

 through Henking's idea of a conjugation of 

 the chromosomes (the term introduced by 

 Boveri), proved to be true by Eueckert (1891). 

 As the final word of all his studies during 

 these years may be regarded his article 

 " Befruchtung " in Merkel und Bonnet's 

 Jahresbericht, 1891, where he reviews the 

 whole field in his keen and masterly way. It 

 is of special importance that here were pub- 

 lished the first figures of the process of dim- 

 inution of the chromosomes, some years previ- 

 ously discovered by him in the cleavage cells 

 of Ascaris and fully understood in its impor- 

 tance for the doctrine of the Keimplasma. 



It has been stated already how keenly Boveri 

 felt the necessity of applying experimental 

 methods to the study of cytology. His first 

 papers in this direction were published in 1888 

 and 1889. The latter especially gave a great 

 impetus to our science, his famous report, 

 " TJeber einen geschlechtlich erzeugten Organ- 

 ismus ohne muetterliche Eigenschaften." 



The brothers Hertwig had succeeded in rear- 

 ing fragmented eggs of Echinoderms up to the 

 gastrula stage and had been able to fertilize 

 enucleated fragments of sea-urchin eggs. 

 Boveri conceived the very ingenious idea of 

 using this method, to determine whether or 



