VALUE OF THE ATTRACTION-SPHERE. 159 



either in the ova or in the spermatozoa, but to arise imme- 

 diately after fertilisation, as the first organs evolved during 

 individual ontogeny. The increasing amount of evidence 

 which bears directly on this point has produced no other 

 result so far than that of equally increasing the already wide 

 divergence of opinion respecting the origin of the spheres 

 in the first instance. Some observers, like Vejdovsky (10) 

 (in the case of Rhinchelmes), believe that they enter with 

 spermatozoa already pre-formed into the Qgg, having appar- 

 ently arisen from pre-existing spheres in the spermatogenesis. 

 Julin (11) regards the possession of a sphere as a distinctive 

 character of the male cell of Stylopsis grassolaria, and goes 

 so far as to make this a mark of distinction between ova and 

 spermatozoa in general. 



The researches of Balbiani (12) show the Dotterkern, 

 "Vitelline nucleus" of Arachnid eggs, to be homologous 

 with what he terms the " Nebenkern (Centrosome of 

 Platner)," i.e., of the attraction-sphere of these eggs, and to 

 arise from the nucleus ! as a little bud, which, although 

 sometimes dividing, rapidly becomes " hypertrophid " and 

 functionless, constituting a homological stepping-stone be- 

 tween those forms where the sphere appears to be present 

 solely in the male, and those in which it is present only in 

 the female. 



Boveri in his last publication maintains that there are 

 neither centrosomes nor asters related to the mitoses which 

 form the polar bodies in the ovigenesis of Ascaris, and he 

 uses this observation to support his theory that the spheres 

 are derived entirely from the male. 1 



In the spermatogenesis of certain mammalia and elas- 

 mobranchs I (13, 14) have found bodies answering to the 

 centrosomes to be incorporated with the mature spermatozoa, 

 and Field (16) seems to have arrived at similar conclusions 

 with respect to the spermatogenesis of echinoderms. Fick 

 (17) figures a sphere related to the intruding spermatozoon 



1 While at the Naples laboratory last spring, my friend Dr. Morton 

 Wheeler showed me preparations of the eggs of myzostoma with beautifully 

 denned centrosomes at the apices of the polar-body spindles, so that 

 Boveri's view is not of universal application. 



