In contrast to normal and spayed cba females, spayed and androgenized cba females are as effective as normal cba males in blocking ovo-implantation in newly mated P mice. Hence it is concluded that the pheromones involved in producing the block to ovo-implantation are associated with androgens either directly, or indirectly through some androgen-dependent gland. Recent reports (Dominic, 1964, 1965) suggest that urine is the immediate source of the pheromones produced by male mice which cause the olfactory block to pregnancy in newly mated females (Bruce, 1960; Parkes & Bruce, 1961). Urine of grouped prepuberally or post-puberally castrated male mice retains the pregnancy blocking capacity to some extent (Dominic, 1965) but in each individual this capacity may be too far diminished by castration to be effective when the female is exposed to a single male (Bruce, 1965). The present report deals with experiments conducted to determine the capacity of normal, spayed or spayed and androgenized alien (CBA) females to block ovo-implantation in newly-mated albino mice belonging to the Parkes () strain. The spayed CBA female was androgenized by subcutaneous implantation of a pellet of testosterone (4-androsten-17-ol-3-one propionate, supplied by Steraloids, Ltd, Croydon) weighing about 50 mg. Tests were started about 2 weeks after implantation. The female was separated from the stud male after mating (i.e. vaginal plug found) and exposed on Days 1 to 3 post coitum to one of the following situations: (1) housed in the proximity of a normal CBA female, the latter confined in an expanded metal corral in the box housing the mated female; (2) similarly housed in the proximity of a confined spayed CBA female; (3) housed in the proximity of a confined spayed and androgenized CBA female; (4) exposed to fresh urine from twelve spayed and androgenized CBA females; (5) exposed to the same situation as in (4) except that urine from androgenized CBA females was prevented from reaching the newly mated females (urine controls) ; (6) housed in boxes with empty corrals; and (7) left undisturbed. Daily vaginal smears were examined from all test females up to Day 7 post coitum and a return of vaginal cornification within this period was taken to indicate a blocked pregnancy. The results are sum¬

Spermatozoa were observed in all parts of the genital tract in females killed in January, February, March and April although copulation occurs only until early February. The spermatozoa were arranged linearly with their heads orientated towards the epithelial lining.

Experiments were designed to elucidate the mode of transmission of the male-originating pheromones involved in the induction of estrus (the Whitten effect) and in implantation failure (the Bruce effect) in mice. The Whitten effect was induced in unisexually grouped females by exposure to corralled males, and also by corralled males housed within a perforated cage (which prevented physical contact of the females with the male-originating pheromone). The results suggest that the pheromone involved in the Whitten effect is volatile (airborne). Implantation failure occurred in a significantly high proportion of newly inseminated females when they were individually confined in corrals and housed below corralled alien males. By contrast, implantation failure was significantly reduced when corralled females were housed above corralled alien males. The results indicate that the male-originating pheromone involved in the Bruce effect is nonvolatile and acts on the females through contact. It is suggested that the pheromone involved in the Whitten effect is distinct from the one involved in the Bruce effect.

The pituitary gland of the musk shrew, Suncus murinus L. was studied with special reference to the cytology of the adenohypophysis. In addition to the agranular cells (chromophobes ), seven morphologically and tinctorially distinct Nchromophilic cell types (four mucoid and three acidophilic) were observed in the pars anterior. These cells have been tentatively named as types one to seven. On the basis of their morphology, topography and staining reactions, cells of types one to six were compared, respectively, with the TSH, FSH, ICSH (L,H), LTH (prolactin), STH and ACTH cells of other mammals. The identity of type 7 cells could not be determined. Although mucoid cells (types 1, 2) art: more concentrated in the rostroventral region of the pars anterior, a definite "zona tuberalis" seems to be lacking. Since the musk shrew is not a seasonal breeder, the gonadotropic cells (types 2, 3 ) of the adenohypophysis do not seem to fluctuate in structure during the different times of the year. However, conspicuous hypertrophy, hyperplasia and intense secretory activity of type 4 cells during pregnancy and lactation reinforces the postulation that these cells are lactotropic in function. Follicular cysts and colloid in the residual cleft were observed in a few instances. Their possible origin and significance are discussed.Knowledge cif the morphology and cytology of the hypophysis in several groups of mammals has been enriched immensely i n recent years. (Purves, '61, '66; Herlant, '64, '65; Hansi:rom, '66; Girod, '66; Allanson and Parkes, '66). However, only scanty inform ation is available on the order Insectivora, except for the mole (Herlant, '64; Holmes, '66), desman (Herlant, '64) and hedgehog (e.g., Girod et al., '66, '67). The family Soricidae of this order does not seem to have received any attention, the (only study having been confined to brief description of the hypophysis of the short-tailed shrew, Blarina (Dawson, '63; Hanstrom, '66). The present paper presents a detailed anatomical description of the hypophysis and a comprehensive account on the cytology of the adenohypophysis of the musk shrew, Suncus ,murinus L. Banaras Hindu University c a m m s and adjacent areas were used. Included were 50 females in different stages of gestation, 12 pregnant and concurrently lactating females, 8 lactating females, 90 non-pregnant females and nearly 100 males. Most of the animals were sacrificed within 12 hours of capture; some were maintained in the laboratory for varying periods before sacrifice. Conspicuous seminiferous tubules visible through the tunica albuginea of the testes, and the presence of spermatozoa in the testes and the genital tract, were taken as indicators of sexual maturity in the male. Since some animals weighing 28-35 gm were pregnant, females weighing 40 gm or more were regarded as being sexually mature. The condition of the mammary glands, uteri and ovaries were considered in assessing the sexual maturity of the female. Pregnant females were classified into three groups (those of early, ...

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