THE HYBRID CHARACTER OF THE GAMETES AND REPRODUCTIVE TRACTS OF THE AFRICAN SHREW, MYOSOREX VARIUS, SUPPORTS ITS CLASSIFICATION IN THE CROCIDOSORICINAE

The Soricidae are generally considered to comprise two subfamilies - C rocidurinae and Soricinae - each of which has distinctive reproductive characteristics. Although Myosorex varius is classified as a crocidur ine, the features of its reproductive system call that classification into question. Compared with three other shrew genera, Myosorex exhibi ted a number of specific features including a relatively prolonged tim e (about 22 h) for ovulation to be induced by hCG injection and the sm allest diameter (75 mu m) recorded for any mammal egg. Moreover, the r elative testis mass and the number of epididymal spermatozoa were some what greater than in some other shrews studied recently. However, many reproductive features in Myosorex have a 'hybrid' character. The glan s penis has spines similar to those evident in crocidurines but absent in soricines, yet the accessory sperm storage site, midway along the vas deferens, is similar to that in soricine shrews. The ultrastructur e of Myosorex spermatozoa was primarily soricine, despite an unduly la rge acrosome, which reaches its apogee in the Crocidurinae. Whereas th e Fallopian tube displays a crocidurine-type isthmus characterized by deep crypts throughout, the ampulla is richly endowed with ciliated cr ypts, which in soricines contain spermatozoa. The first polar body per sists in the Myosorex ovum, as it does in the soricines Cryptotis and Blarina, but not in the crocidurine Suncus and Crocidura. However, the cumulus oophorus of Myosorex appears largely crocidurine by virtue of its persistent intercellular junctions, long term stability, and the absence of a matrix, lacking only the unique perizonal spate that fina lly characterizes the cumulus of the crocidurines, Suncus and Crocidur a. The ''hybrid'' character of the reproductive system of Myosorex is more consistent with the proposal that the genus is a survivor of a pr imitive subfamily - the Crocidosoricinae - from which present day Sori cinae and Crocidurinae have arisen.