486 
MR. W. H. CALDWELL ON MONOTREMATA AND MAR SU PI ALIA. 
Fig. 8. Hypsiprymnus. —From uterus, ‘4 mm. in diameter : sh, shell membrane; vm, 
vitelline membrane; urn, coagulum; bl, blastopore ; ep, epiblast ; hy, 
hypoblast. (Cf fig. 2.) 
PLATE 31. Zeiss, oc. 2, obj. c. : cam. luc. 
Four sections through the germinal disc of Echidna and Ornithorhynchus. The 
violet corresponds to the distribution of the more active protoplasm. The yellow yolk 
spheres are coloured buff. 
Fig. 1. Echidna. —Median section through the germinal disc of an unsegmented ovum 
taken from the lower part of the Fallopian tube, measuring 3'2 mm. in 
diameter : sh, shell; alb, albumen ; vm, vitelline membrane. 
Fig. 2. Echidna. —Stage of four segmentation nuclei. Lateral section through one 
pair of nuclei made in a plane at .right angles to the first furrow ; ovum 4'5 mm. 
in diameter : n x , nucleus of smaller area ; n 2 , nucleus of larger area. 
Other letters as in fig. 1. 
Fig. 3. Ornithorhynchus. — From open end of Fallopian tube, 2’6 mm. diameter. Stage 
of eight segmentation nuclei : ch, pro-albumen. 
Fig. 4. Echidna. —From uterus, 5 mm. in diameter. Median vertical longitudinal 
section through germinal disc : urn, coagulum ; ep, epiblast; hy, hypoblast. 
Other letters as in fig. 1. 
