262 J. E. S. MOOEE, 



investigation^ an essential agent seems to be two centres of 

 an alternately attractive and repulsive nature (centrosomes) ; 

 but concomitantly witb, and independently of, their opera- 

 tion, other and no less important changes accrue within 

 the cell, perhaps most notably, the evolution of the fine 

 chromatic reticulation of the resting nucleus into a limited 

 number of chromosomes at the nuclear periphery, their 

 number being constant for any particular species — a fact 

 making them of great practical importance in all questions 

 relating to heredity. 



Now I wish to call attention to some points in the sperma- 

 togenesis of Branchipus, which may appear to throw much light 

 on portions of these successive stages; and although it is at 

 present hopelessly inadequate to illuminate the greater pro- 

 blems which arise from it, I have taken extra trouble to be sure 

 of my ground here, because I conceive that the existing theo- 

 retical solutions of these problems must one day find powerful 

 confirmation or the reverse, in a true appreciation of the 

 character of the processes which underlie the karyokinetic 

 metamorphosis. 



Spermatogenesis. 



The male gland in Branchipus is a rather straight biramous 

 tube extending up the tail, and a short distance further up the 

 body. If spermatozoa are free in the lower portion all the 

 stages of spermatogenesis are visible as we pass up. The 

 diff'erence in phase amongst the cells may be taken to represent 

 the zones of Hertwig, van Beneden, and Julin.^ 



The spermatocytes, however, break away from the walls in 

 groups (fig. 21), their individual components being all in the 

 same phase. But as this phase, characteristic of each group as 

 a whole, is not often similar to those on either side of it, we 



' " Nouvelles recherches sur la fecondation et la division mitosique chez 

 I'ascaride megalocephale," ' Bullet, de I'Academie Royal de Beige,' 3me ser., 

 c. xix, 1887. " Befruchtung und Theilung des thierischen Eies," ' Morph. 

 Jahrb.,' 1875. 



