GERM CELLS IN THE ARTHROPODA 157 



added in the figure from a part of the oocyte three 

 sections away. A still further stage of fusion is 

 indicated in Fig. 47, D. 



In all these cases and in fully developed eggs 

 there is a distinct "waist line" which can be ac- 

 counted for upon the view that two oocytes fuse end 

 to end as above described, the narrow part corre- 

 sponding to the region of union. The conclusion 

 seems warranted, therefore, that every egg when laid 

 consists of two oocytes which have united end to end, 

 the posterior or older oocyte being provided with 

 keimbahn-chromatin derived from the chromatin of 

 its nucleus, and the anterior supplied with a nucleus 

 which has arisen from the disintegration of a spindle 

 similar to that from which the keimbahn-chromatin 

 originated. 



A number of references are present in literature to 

 what have been termed " uterine," " disappearing," 

 or "aborting" spindles. Such a spindle was first 

 noted by Selenka (1881) in the turbellarian, Thysano- 

 zoon diesingii. Here apparently a completely de- 

 veloped maturation spindle was observed in the 

 fully grown eggs after they had entered the uterus ; 

 then, just before the metaphase of mitosis, the spindle 

 broke down and the nucleus returned to a resting 

 condition. This same nucleus later gave rise to 

 polar bodies as in the eggs of other animals. Similar 

 aborting spindles have been described by Lang (1884) 

 in several species of polyclads, by Wheeler (1894) in 

 Planocera inquilina, by Gardiner (1895, 1898) in 

 Polychoerus caudatus, by Surface (1907) in Planocera, 



