HUBRECHT. 
Fig. 1. Cleavage stage of the dog (after Bonnet, ‘97). The mother cells 
ck of the embryonic knob, centrally situated, have stained more deeply than 
the trophoblast cells (¢”). — Fig. 2 and 3. Sections through two different early 
cleavage stages of Tupaja javanica. In this case the trophoblast cells, ¢r are 
more deeply stained than the mother-cells of the embryonic knob e& — Fig. 4 
and 5. Sections through early stages of the opossum (after Selenka, 87). In Fig. 4 
there are thirteen trophoblast cells ¢ and one mother cell of the embryonic 
knob e&, in Fig. 5 the latter has given rise to a mass of cells which begins to 
project on the surface /e#) and in which the differentiation of entoderm cells has just 
commenced. — Tig. 6, 7, 8. Three sections of different developmental stages 
of the bat (after van Beneden, ‘99). In Fig. 6 the differentiation between tro- 
phoblast cells ¢ and embryonic knob is again expressed in the staining; in Fig. 7 
the embryonic knob (Z) is not yet separated into ectoderm /e%) and entoderm 
(en) as it is in Fig. 8. 
