496 



R. MATTHEY ET F. PETTER 



nombre pair de SM (6 — non observés — x8 et 8x 10). Un mâle présente une 

 fusion centrique abaissant le nombre 2N à 39. Chez un autre mâle, il y a un tétra- 

 valent à la métaphase I, ce qui s'explique par une translocation entre deux SM 

 non-homologues. Le chromosome X de M. dunni est un grand métacentrique à 

 bras subégaux. 



L'analyse comparée des génomes de M. booduga et de M. dunni montre 

 qu'une fraction importante des trois paires les plus grandes de M. dunni a été 

 répartie, à la suite de ruptures et de translocations répétées, entre les autosomes 

 des paires 6 à 17 de M. booduga. 



Il n'existe aucune indication de parenté étroite entre ces Souris indiennes et 

 les Souris africaines des groupes minutoides, tenellus et bufo-triton. 



SUMMARY 



The analysis of 15 pigmy-mice from a rice-field in the neighbourhood of 

 Madras (India) was performed independantly by a taxonomist using the methods 

 of the classical Systematics (F. Petter) and by a cytologist (R. Matthey). Their 

 results are in full agreement: the sample includes spécimens of two species which 

 appear as very akin but can be distinguished through some characters of the 

 teeth and of the pigmentation, more easily through their chromosome-comple- 

 ments. After comparizon with the types which are kept in the British Muséum 

 13 spécimens belong to the species Mus dunni Wroughton and two to the species i 

 Mus booduga Gray. 



M. booduga has the same complément as M. musculus : 2N = 40, N.F. == 

 40. Autosomes and sex-chromosomes are also acrocentric. 

 M. dunni : 2N = 40. The N.F. varies from spécimen to spécimen: 49, 50, 51 and 

 52 have been registered. This polymorphism is due to the présence of 7, 8, 9 or 

 10 submetacentric chromosomes (SM). Thèse numerical variations in striking 

 contrast with the constancy of the diploid number can be explained as resulting 

 from pericentric inversions. The spécimens with an odd number of SM (7 or 9) 

 show an heteromorphic pair associating a SM and an acrocentric chromosome. 

 Thèse spécimens must arise from crosses between the bearers of différent complé- 

 ments (6 — not observed — x 8 and 8x10). 



In one maie a centric fusion reduces to 39 the diploid number. 



In another maie, we find a tetravalent at the first métaphase which oviously 

 must resuit from a translocation between two no-homologous SM. The big 

 X-chromosome is metacentric with almost equal arms. 



The comparative cytology of both species shows that an important fraction 

 of the three longest pairs of M. dunni is distributed through many ruptures and 

 translocations between the pairs 6-17 of M. booduga. 



