324 EDWIN G. CONKLIN 



These 'polar bodies' may be caused to form at any point on 

 the surface of the egg, without changing in the least the position 

 of the ectodermal pole. It may be doubted whether such cells 

 which are formed at some distance from the ectodermal pole can 

 properly be called 'polar bodies,' not merely because they do not 

 mark a specific pole but also because they are larger than normal 

 polar bodies, they frequently contain different ooplasmic sub- 

 stances such as oil and yolk as well as cytoplasm, and they 

 doubtless sometimes contain that pole of the spindle and its 

 chromosomes which would have remained in the egg if the polar 

 bodies had been formed normally; that is these abnormal cells 

 differ both in position and in constitution from normal polar 

 bodies. 



On the other hand they show certain resemblances to polar 

 bodies, viz., they I'arely divide and never undergo regular cleav- 

 age, and most important of all they are formed by those peculiar 

 nuclear divisions which are known as the maturation divisions. 

 Since the notable work of 0. Hertwig ('90) and Boveri ('91) in 

 which they pointed out the parallelism between oogenesis and 

 spermatogenesis it has been universally recognized that the two 

 maturation divisions are homologous in oogenesis and spermato- 

 genesis and that consequently the cells which are formed by these 

 divisions are comparable. The cells formed by the first matura- 

 tion divisions are known as 'second oocytes' or 'spermatocytes,' 

 those formed by the second maturation division as 'ootids' or 

 'spermatids.' In normal eggs three of these ootids are very 

 small and are known as 'polar bodies,' while the fourth is large 

 and is called the 'egg;' it is evident from the manner of their 

 origin that the polar bodies are rudimentary eggs, a view which 

 was first set forth by Mark ('81). When eggs have been sub- 

 jected to pressure or to centrifugal force, all of the ootids may 

 be of approximately the same size, although only one of these 

 cells develops; the fact that three of these cells do not always lie 

 at the animal pole of the cell which develops indicates that the 

 term 'polar body' in such cases is a misnomer. But at least all 

 four cells are ootids and for the sake of simplicity of expression 

 it seems desirable to call these ootids, which do not develop and 



