Second, spermatozoa with a rounded head and a filamentous tail extending from it, as in the common perch and some other fishes. Next, those with oblong heads, found in the domestic cock. Fig. 156. Spermatozoa of the cock (Gallus domesticus). In some birds, as sparrows and finches, the heads of the spermatozoa are wavy, as seen in the drawing. Fig. 157. Mother cell with a bundle of spermatozoa from Fringilla domestica. In rats and mice the spermatozoa have very long tails, and heads of very peculiar form. Fig 158. B A. Spermatozoa of the rat. B. Of the common mouse THE OVARIES of the female are composed of a dense fibrous stroma, in which numerous small pellucid bodies (Graafian follicles) are imbedded. The entire organ is invested with a fibrous coat and a covering of peritoneum. On making a section of an ovary, the Graafian vesicles will appear most numerous towards the circumference. A single vesicle may be examined by dissecting a specimen from the ovarium of a cow, placing it in a little water on a slide, and applying sufficient pressure with the covering glass to flatten it slightly. The structure of the capsule and the portion of the ovum within it may sometimes be made out in the fresh specimen, but sections of an injected and hardened ovarium are much to be preferred. To obtain a single ovum for examination, a large Graafian follicle should be punctured and the fluid allowed to flow on to a piece of glass. The ovum should then be sought with a lens or under the low power, and, when found, covered with the thin glass and examined with the high power. The drawing indicates what the student should see in a good specimen. Human ovulum, from a middle-sized follicle; magnified 250 times. a. Vitel- After the escape of the Graafian follicle from the ovarium, the space it occupied is filled up with a yellowish-white substance, termed the corpus luteum. The masses thus formed are very apparent upon the cut surface of the ovarium, particularly from an animal that has been frequently pregnant. The structure of the true corpus luteum, which in every respect except size resembles the false, may be demonstrated by teazing out a small portion in water upon the slide, and covering it, previous to examination with a high power. The elements are found to be nucleated cells, which become partly transformed into imperfect connective tissue. Sections of these bodies may be made in fresh specimens with the double knife, or from those hardened in chromic acid with a razor. The section should be placed in water on the slide and covered in the usual way, and examined with the low power. The various parts which should be seen in a good section are presented in the illustration. Sections of two corpora lutea, of natural size. The upper one represents a THE MAMMARY GLANDS, or lacteal glands, exist in the male animal as rudimentary organs, but in the female they are developed fully and possess the function of secretion. In structure the lacteal glands correspond to the pancreas and salivary glands, being composed of lobes formed by the union of small lobules, which are constituted of gland vesicles. These elements are united by white fibrous tissue. The structure of the mammary glands is best studied by teazing out portions on the slide, and in sections of hardened and injected preparations. Specimens which are prepared by being hardened in alcohol or by boiling may be rendered sufficiently transparent by immersion in glycerine. The arrangement of the lobules is seen in the illustration. Some of the smallest lobules of the lacteal gland of a puerperal woman, Milk is to be examined in the manner adopted for other fluids, a drop being placed in the centre of the slide and covered with the thin glass. Care must be taken that the otherwise the elements will not be distinct. film is not too thick, When properly pre pared the fluid will be found to consist of a transparent medium, in which numerous oil globules are floating. In the milk secreted immediately before and after parturition, a number of compound corpuscles, called colostrum corpuscles, are found. Some little care is necessary in the examination of milk, to avoid confounding small aggregations of milk globules with colostrum corpuscles, which are surrounded by a fine membrane, or cell wall, as shown in the illustration, and particularly at c. The aggregations of the ordinary milk globules are usually larger than the colostrum corpuscles, and their outline is less regular; but the absence of any defined wall round the mass will be the most reliable and |