568 Messrs. J. E. S. Moore and G. Arnold. Existence [Dec. 13, 



types h and / are present together in rats in such a manner as to suggest that 

 they are really distinct entities. 



In rats we have said that the number of the pre-synaptic chromosomes is 

 32 and the number of gemini is 16. These latter bodies are grouped into 

 six varieties, and consequently the number of each variety in rats must be 

 unequal. 



If in rats in a large number of division figures the maximum number of 

 all the six varieties of gemini are counted, as was done in Trijon, the results 

 are as follows: a— 4, 1—2, c— 4, e— 2 J— 2, h—2* 



Upon comparing the above results with similar results in man we find 

 that here the varieties remain the same as in rats, but the relative numbers of 

 these varieties are again changed (see fig. 6, Plate 25, and table, p. 566), the 

 arrangement in man being as follows : a — 2, b — 2, c — 6, e — 2,/ — 2, h — 2. 



For any one species the numbers of types of gemini, so far as we have gone, 

 appears to be constant, and the same types are retained in the case of fairly 

 remote genera, such as Homo and Mus ; but in these genera the relative 

 numbers of the different kinds of gemini may vary with, or independently of, 

 the number of the premaiotic chromosomes. 



Passing from the above vertebrate examples to the old arthropodean type 

 Periplaneta we find, as fig. 5 and the table on p. 566 will show, that here the 

 number of the types pf gemini is reduced from six to five. 



Upon consideration of the table it will be seen also that three of the 

 amphibian and mammalian types are retained, but no new type is added, and 

 two of the types common to both the other groups are altogether wanting. 



In Periplaneta there are 32 premaiotic chromosomes and 16 gemini, so 

 that here, as in the case of man and rats, the number of similar forms must 

 be unequal. 



Counting the maximum number of any type in a number of cells, as was 

 done in the former cases, we get the relative number of the five types in each 

 cell as follows: a— 4, b— 4,/— 2, g—4, h—2. 



The possible bearing of the above observations upon the various existing 

 theories of hereditary transmission, and especially in relation to the Mendelian 

 hypothesis, will be obvious enough ; but we feel a great reluctance at the 

 present time in any way to augment the obscuration of the facts by putting 

 forward crude theoretical anticipations. 



What appears to us of first importance is the recognition of the actual 

 existence of permanent structural types in the gemini of different forms. 

 Secondly, it would appear that in any particular form the number of gemini 



* It is an interesting and important fact that the number of premaiotic (somatic) 

 chromosomes is not the same in rats as in mice. In the latter the number is 24. 



