BLACKMAN: the spermatogenesis of scolopendra. Ill 



plasm. Such may likewise be the case, it appears to me, with regard 

 to the same structures in cells which show a more marked alveolar 

 nature. It seems probable that in these cells the astral fibres follow 

 the course of the alveolar boundaries, and in the fixed material cannot be 

 differentiated from the unmodified cytoplasm, i. e. alveolar walls, through 

 which they pass. My observations relative to the question, whether 

 the astral rays are of a fibrillar character or merely the visible indica- 

 tion of diffusion currents, all point to the former condition. That 

 the astral rays in many eggs at least are not diffusion currents, but 

 more permanent structures, would seem to be demonstrated by the ob- 

 servations of MacFarland ('97), Griffin ('99), Lillie ('98), Coe ('99), 

 and Smallwood (:04), who show that the old astral rays still persist for 

 a considerable time and continue to converge toward the same point, 

 after the divided centrosome and new asters have moved away and 

 taken up a new position. If the rays were mere diffusion currents, it 

 seems highly improbable that they would persist so long. On the 

 other hand, if they are fibres, it would naturally require considerable 

 time for them to be broken down and their substance redistributed 

 around new centres. 



When we inquire into the function of the aster, we immediately find 

 ourselves concerned with the problems of cleavage, so closely is the 

 aster associated with this phenomenon. I do not, at this time, wish to 

 enter upon the question of the mechanics of mitosis, since already 

 many explanations, more or less unsatisfactory, have been attempted, 

 and it is evident that our knowledge of mitosis is not yet sufficiently 

 complete to serve as a basis of a theory which will explain all known 

 phenomena of cytoplasmic division. However, as I have shown in 

 the body of this paper (p. 50), my observations lend themselves more 

 readily to the older, well-known hypothesis of cell division by fibrillar 

 contractility. I have considered the subject in sufficient detail at that 

 place, and will not enter into further discussion of it here. 



3. Spermatid Metamorphosis. 



The metamorphosis of the spermatid, while probably not as important 

 from a theoretical point of view as the phenomena connected with the 

 spermatocyte division, nevertheless otters many points of interest and 

 has been the subject of much careful investigation. It is not my pur- 

 pose to review the literature in any extensive manner, for within the 

 last few years this has been done by a number of writers, the most notable 



