OVULATION INDUCTION AND GAMETE TRANSPORT IN THE FEMALE TRACT OF THE MUSK SHREW, SUNCUS-MURINUS

The musk shrew Suncus murinus was studied with regard to induction of ovulation, the genesis and role of the vaginal copulation plug, and th e behaviour of gametes acid embryos within the Fallopian tube. Ovulati on occurred about 15 h after ejaculation, which required a mean of 5.2 (range 2-10) intromittent thrusts. Since ovulation occurred also afte r five thrusts without ejaculation, and after ejaculation without plug formation or sperm deposition, the primary stimulus for this seemed t o be the thrust of the penis, the glans of which was covered by a dens e field of spines. Neither vasectomized nor prostatectomized males for med a plug at ejaculation, and in the latter case the mean number of s permatozoa reaching the isthmus of the Fallopian tube, the number at t he ampullary fertilization site and the rate of fertilisation were low er than in females mated to normal males. Thus both the vesicular glan d on the vas deferens and the prostate are essential for formation of the copulation plug, which appears to enhance sperm transport within t he female tract. At ejaculation, less than or equal to 10(6) spermatoz oa were incarcerated by the plug in the anterior vagina for 6-7 h, by which time a maximal population of several hundred had become establis hed in posterior crypts of the isthmus of the Fallopian tube as small groups of free languidly moving spermatozoa. It remains to be establis hed whether oviductal crypts in this and other shrews have a storage f unction for spermatozoa or sequester spermatozoa and so regulate the n umber that reach the fertilization site. Very few spermatozoa reached the ampulla of Suncus. Generally, only one or two spermatozoa had reac hed the ampulla by 4-5 h, and often less than ten had done so by 5-13 h after ovulation. As a probable correlate, few eggs were penetrated d uring the first 5 h, with a frequent delay of 10-13 h before most eggs were fertilized. Thereafter, unfertilized eggs were transported throu gh the oviduct at the same rate as developing embryos, which entered t he uterus about 85 h after ovulation at the 32-cell stage. There were highly significant differences between the larger KAT/SK strains and s maller OK strain with regard to Fallopian tube length (mean 6.9 mm ver sus 9.7 mm), as well as the rates of hCG-induced ovulation (5.6 versus 3.25) and of unilateral ovulation (6% versus 50%).