632 



the act of conjugation of the chromosomes the germ cells enter upon 

 a period of tremendous metabolic activity, in the case of the ovocyte 

 at least the most intense and prolonged in the whole germinal cycle, 

 namely the growth period preceding the first maturation mitosis. A 

 good teleological explanation of the pairing of the chromosomes has 

 been given by Sutton (1903); but I dealt with the question of the origin 

 of this process, and the idea of rejuvenation explains the facts as well 

 as any view yet offered. 



As to the "types" of reduction distinguished by Prof. Haeoker, I 

 thoroughly agree with him that there is no well proven case where 

 both mitoses are equational; and I believe that we may have a very 

 reasonable doubt as to whether in any Metazoan both maturation divi- 

 sions are equational. For those cases where there is a reduction 

 division (a separation of entire univalent chromosomes from each 

 other), I have suggested that for the particular division in which this 

 is effected the terra "heterotypic" mitosis may be employed. Flem- 

 ming (1887) introduced this word for those cases (spermatogenesis 

 of Amphibia) where the chromosomes differ in form from all other 

 generations (in the particular case, ring shaped). Now though Flem- 

 ming believed that the split or space in each such chromosome 

 represents an equational split, and that therefore their mode of division 

 is equational and not reductional (a view which I, 1903, 1904, have 

 endeavoured to prove is erroneous), we may nevertheless apply the 

 term heterotypic to each reduction mitosis, because these are the 

 particular mitoses where the form of the chromosomes differs from 

 those in any other divison of the germinal cycle. This is sufficient 

 answer to Prof. Haecker's foot-note on p. 211. A heterotypic mitosis 

 is one where the chromosomes are formed and behave differently from 

 any other mitosis, just because they are forjned difi"erently; and it is 

 of no importance at all whether they have ring form or not, for in the 

 same cell some of the bivalent chromosomes may be in the form of 

 dumb-bells, others of V's H's, of two parallel rods, or of rings (e. g. 

 some Hemiptera, Peripatus). 



On p. 229 of the review under discussion we read as the describer 

 of the egg of Crepidula the name of Calkins; this is of course a 

 mistake for Conk lin. 



Finally a word as to Prof. Haecker's own interpretations of the 

 ovogenesis of Cyclops. Riickert (1894a) concluded from the study of 

 several species of Copepoda that the number of chromosomes is re- 

 duced one half before the first maturation mitosis; that the first matura- 

 tion is an equation division and the second reductional. And in his 

 review (1894b) on reduction Riickert states, p. 576: »Alle genaueren 



