54 EDMUND B. WILSON 



classes having the peculiarities heretofore described). 2 Numbers 

 above 22 arise through the addition of one or more relatively 

 small "supernumeraries," which agree in behavior with the small 

 idiochromosome, of which they are probably duplicates. None 

 of my own material (53 individuals, of three species) showed less 

 than 22 chromosomes, and at least one small idiochromosome was 

 present in all. In all of Montgomery's material of M. terminalis, 

 however (9 individuals), this chromosome is absent, the sperma- 

 togonial number is but 21, and the large idiochromosome appears 

 without a synaptic mate as a typical odd or accessory chromosome. 

 The foregoing results were based on the study of 62 individuals 

 in all, representing the three species, terminalis, femoratus and 

 granulosus. In February, 1909, 1 took at Miami, Fla., two addi- 

 tional male specimens of femoratus, quite typical in structure, 

 and closely similar in external appearance. One of these (No. 63) 

 is an ordinary 23-chromosome form with one large supernumerary 

 (like Nos. 13 or 48 of the general list given in " Study V") and is 

 only of interest for comparison with the other individual. The 

 latter, hereinafter designated as "No. 64," shows a different 

 chromosome-combination from any heretofore seen in this genus 

 or elsewhere. The diploid groups (spermatogonia) contain 22 

 chromosomes; but both these groups in themselves and their 

 history in maturation proves most clearly that they are not the 

 same as in the typical 22-chromosome forms, differing from the 

 latter in respect to the idiochromosom.es and the m-chromosomes. 

 In the typical forms there are, as stated above, two of each of 

 these chromosomes. In No. 64, on the other hand, there are three 

 m-chromosomes and but one idiochromosome (the large), the 

 latter appearing as a typical odd or accessory chromosome, as in 

 the material of Montgomery; thus, 18 autosomes + 3 m-chromo- 

 somes + 1 odd chromosome = 22. That this is the true interpre- 

 tation of the facts is demonstrated by the behavior of these respec- 

 tive chromosomes in the maturation-process. I would emphasize 

 the fortunate fact that both testes of the animal show excellent 

 fixation and staining (strong Flemming, iron haematoxylin) and 

 that they contain multitudes of division-figures which demonstrate 



* Ibid: '056, 05c, '06, etc. 



