OF MONOTREMATA. AND MARSUPIALIA. 
485 
PLATE 29. Zeiss, oc. 2, obj. yg- homogen. : cam. luc. 
Fig. 1. Echidna. —Small portion of a section through the ovarian ovum, measuring 
•32 mm. in diameter. 1st period : fe, follicular epithelium ; vm, vitelline 
membrane; zr, zona radiata; y, yolk granules ; y 2 , white yolk; o, oil 
globule ; h, basilar membrane. 
Fig. 2. Echidna. —Small portion of a section through the ovarian ovum, measuring 
1 mm. in diameter. 2nd period : lettering as in fig. 1. 
Fig. 3. Echidna. —Small portion of a section through the nearly mature ovarian ovum. 
Beginning of 3rd period : lettering as in fig. 1. 
Fig. 4. Echidna. —Small portion of a section through the ripe ovarian ovum, measuring 
3 mm. in diameter. 3rd period : ch, pro-albumen. 
Fig. 5. Pliascolarctos cinereus .—Medium section through a nearly mature ovarian 
ovum taken from the “liquor folliculi” of a follicle measuring 9 mm. X 6 mm. : 
fe , follicular epithelium ; vm, vitelline membrane ; gv, germinal vesicle. 
PLATE 30. Zeiss, oc. 2, obj. yg- homogen. : cam. luc. 
Fig. 1. Ornithorhynchus. Small portion of a section through the segmenting ovum, 
taken from the open end of the Fallopian tube, measuring 2’6 mm. in 
diameter: ch, pro-albumen ; vm, vitelline membrane. 
Fig. 2. Echidna. —Small portion of a section through the segmenting ovum taken 
from the uterus, and measuring 6 mm. in diameter : sh, shell; alb, albumen ; 
vm, vitelline membrane ; um, coagulum ; hi, blastopore; ep, epiblast; hy , 
hypoblast. 
Fig. 3. Ornithorhynchus .—Small portion of a section through the segmenting ovum 
taken from the uterus, and measuring 6 mm. in diameter : sh, base of shell; 
shy, middle layer of ditto ; sh.,, papillae of ditto. 
Fig. 4. Echidna. —Small portion of a section through the blastodermic vesicle, taken 
from the uterus, and measuring 9 mm. in diameter : sh.,, cones derived from 
papillae of previous stage. 
Fig. 5. Pliascolarctos cinereus. —The 17th section of a vertical longitudinal series of 
35 sections through the segmenting ovum, containing 2 nuclei, taken from the 
uterus, and measuring T 7 mm. in diameter : sh, shell membrane; fe, cells of 
follicular epithelium; alb, albumen; ch, pro-albumen; vm, vitelline mem¬ 
brane; y x , protoplasm, with finest yolk granules; y 2 , white yolk; n, nucleus 
of smaller segmentation area ; n 2 , nucleus of larger segmentation area. 
Fig. 6. Pliascolarctos. —From uterus, *28 mm. in diameter, stage of 4 nuclei: sh, shell ; 
ch, pro-albumen ; alb, albumen ; vm, vitelline membrane. 
Fig. 7. Pliascolarctos. —From uterus, '31 mm. in diameter; lettering as in fig. 6. 
