366 4. Fortpflanzungslehre. 



disappears, and as the spindle is formed the chromosomes re-unite in pairs 

 to form the reduced number of bivalent rings. In the first meiotic division 

 the two members of each bivalent are separated to opposite poles. The second 

 division follows without resting stage; each ehroraosome divides longitudinally 

 and not by the transverse constriction. The transverse constriction seen in 

 the chromosomes in both divisions doubtless corresponds with the apex of the 

 V in somatic mitoses. Occasionally a resting stage intervenes after the stage 

 of synizesis and before the first division, in which the nucleus resembles the 

 germinal vesicle of an oocyte, and in one testis of a hibernating specimen 

 actual eggs were found. In spermatogonial mitoses the chromosomes are 

 from their first appearance short and V-shaped; nothing like the leptotene 

 and zygotene stages occurs. Chromosomes of similar size are always near 

 together in the equatorial plate, so that homologous chromosomes lie approxi- 

 mately side by side. In conclusion the author discusses the reality of the 

 parallel conjugation in the zygotene stage, and the meaning of the Separation 

 and re-conjugation of the paired chromosomes, and points out that the trans- 

 verse constriction of the Univalents in diakinesis, which causes tetrad-like 

 forms when the second pairing takes place, may explain the true nature of 

 the Copepod tetrad, about which there is such divergence of opinion. 



Doncaster (Cambridge). 



1010) Richards, A., The Method of Cell-division in the Development 

 of the Female Sex-Organs of Moniezia. 



(Biol. Bull. 20,3. p. 123—178. 8 plates. 65 figures. Feb. 1911.) 

 Throughout the development of Moniezia Child has described the regulär 

 occurrence of amitosis, not only in the somatic tissues but also in the germ- 

 cells. In the present study, undertaken to test these results, the author was 

 apparently unable to satisfy himself of the occurrence of amitosis at any time 

 or place. As a criterion for the occurrence of amitosis he asserts the neces- 

 sity of „complete series of all stages in the constriction and subsequent divi- 

 sion of the nucleus and attendant cytoplasm". He has failed to find such 

 evidence at any stage of development or in any of the tissues studied, so that 

 rejecting all less complete evidence he comes to the conclusion that in the 

 pre-oögonial, oögonial and cleavage divisions, which are the stages more 

 particularly in question, mitosis is the method of cell-division. The hypo- 

 theses that nuclei may arise de novo or by immigration are likewise rejected. 

 The author admits that the number of mitoses observed in most tissues 

 seems to be inadequate to account for the observed multiplication of cells; 

 but he suggests that mitosis may be of short duration and occur in waves at 

 more or less definite periods depending on some unknown physiological factor. 

 He hardly attempts to explain the appearances which Child describes as 

 favouring the view that amitosis is the method of cell-division, though he 

 quotes interpretations of others, but insists for himself on the necessity for 

 demonstration of all stages of the process to prove its occurrence. 



In his specific conclusions he regards it as undecided whether amitosis 

 or mitosis is the method of cell-division in the vitellarium and female genital 

 ducts, mitosis as a matter of fact not having been observed; but in the early 

 stages of sex-cell development mitosis unquestionably occurs while mitosis is 

 not evident, and „there cannot be the slightest doubt that the cleavage of the 

 ovum takes place by mitosis". Lillie (Chicago). 



1011) Doncaster, L. (üniversity of Cambridge), Gametogenesis of the 

 Gall-fly, Neuroterus lenticularis. Part II. 



(Proc. Royal Soc. B83,B566. p. 476-489. 1 plate.) 



