78 THOS. H. MONTGOMERY jr., 



those lying in the exact plane of division), would become divided. Thus 

 it would seem that the division of the whole chromosome, i. e. of the 

 mass of chromatin and linin, is the important process, division of the 

 individual microsomes occurring or not occurring, depending upon the form 

 of the chromosome. Thus supposing Platner's observations on Sphinx 

 and Fygaera are correct, the longitudinal division of such thick chromo- 

 somes would not result in dividing the microsomes, or at the most, it 

 would result in dividing simply those few microsomes which lie in the 

 plane of division. If it can be proved that the mode of division of 

 a chromosome, i, e. the axis of the line of division, is merely a function 

 of the chromosome, then it would be of no theoretical value whether 

 the division be longitudinal (equation) or transverse (reduction). But 

 it happens that this postulated difference forms one of the main 

 premises of Weismann's theoretical superstructure. On account of 

 the differences observed in different objects, in regard to the modes 

 of division of the chromosomes, it would appear that these differences 

 have no particular theoretical value, but that the halving of the mass 

 of chromatin is the process of importance, the standpoint taken by 

 Hertwig. 



In the two reduction divisions, the chromosomes may split by 

 two longitudinal divisions, by two transverse divisions, by one longi- 

 tudinal and one transverse division, or by one division (longitudinal 

 or transverse) preceded or followed by an elimination division. The 

 facts show clearly that there is no general uniformity in the mode 

 of division of the chromosomes in the reduction mitoses. The long 

 line of observations on different objects show this to be the case, and 

 demonstrates that the expected uniformity does not occur. I am con- 

 vinced of the occurrence of the two longitudinal divisions in Salamandra, 

 having observed essentially the same phenomena in the American genus 

 PlctJiodon; but I have also found that two transverse divisions occur 

 in Pcntatoma, as I trust the observations given is this paper prove. 

 The essential agreement of the observations of Hacker, Vom Rath 

 and RtJCKERT on Copepoda show that in these objects a longitudinal 

 is followed by a transverse division. The facts as they exist in the 

 different objects examined, may be tabulated as follows: 



A. The chromosomes appear in the reduced number 

 in the 1st spermatocytes (or ovocytes). 



1) 2 longitudinal divisions Salamandra, Selachii, Ascaris 



2) 1 longitudinal, 1 equation division Copepoda, Gryllotalpa 



3) 2 transverse divisions Pentatoma 



