14 EDWARD MCCRADY, JR. 



My first recommendations, therefore, for the breeding 

 of opossums are that the breeding pens should have at least 

 50 square feet of floor space, and that the daily diet should 

 include bone meal. The principal foods are meat, milk, and 

 eggs. Vegetables and fruits are eaten, but less avidly. Wild 

 opossums also eat beetles, grubs, and viscera, but apparently 

 these are not necessary constituents of their diet. 



I. PKELIMINARY DATA 



The ovarian egg. The testicular sperm. Mating 



The ovarian egg. Aside from the exceptional frequency of 

 polyovular follicles and poly nuclear ova (Hartman, '36), the 

 general histology of the ovary of the opossum is not signifi- 

 cantly different from that of other mammals. Certainly most, 

 and perhaps all, of these atypical ova and follicles degenerate 

 within the ovary, and so a detailed discussion of them is not 

 necessary in connection with the normal embryology of the 

 opossum. 



Just before ovulation the normal egg (Hartman, '16, '19) 

 is slightly elliptical, the average of the longest and shortest 

 diameters being 0.165 mm. and 0.135 mm., respectively (fig. 1). 

 This is larger than the tubal ovum. The cytoplasm includes 

 a considerable quantity of yolk in the form of granules and 

 fat droplets. These are not concentrated at either pole of 

 the egg, but are principally confined to a rather diffuse 

 spherical layer a little beneath the surface of the ovum 

 (fig. IB, y.g.). The cytoplasm both medial and superficial 

 to this layer is more homogeneous. 



The first maturation division (fig. 1, A) takes place within 

 the ovary. The spindle forms in the superficial cytoplasm 

 usually near one of the ends of the slightly elongate oocyte. 

 The haploid number of chromosomes is eleven, all of which 

 are tetrads in the metaphase of this division. One of these 

 tetrads represents the synapsed X-chromosomes. The first 

 polar body (fig. 1 B, p.b.) is spindle shaped and almost devoid 

 of cytoplasm. It is variable in size, but averages about 

 0.025 mm. in its longest diameter. A distinct zona pellucida, 



