562 A. A. W. HUBRECHT. 



PLATE XLII. 



Figs. 92 — 95. — Four diagrammatical figures to illustrate certain theoretical 

 speculations developed in the text (p. 533). 



Fig. 92. — An amphibian or cyclostomatous gastrula-stage. 



Fig. 93. — A hypothetical transition between the foregoing and the 

 mammalian diagram, fig. 95 (partial perspective). 



Fig. 94. — A sauropsidan gastrula-stage (copied with very slight modifi- 

 cations from Rabl). 



Fig. 95. — A mammalian stage corresponding to the phase which is also 

 represented in the surface views 62 — 64 (partial perspective). Grey 

 and black : trophoblast, embryonic epiblast. Black with white dots : 

 palingenetic hypoblast of the protochordal wedge. Black with parallel 

 stripes : palingenetic hypoblast of gastrula-ridge. Blue : coenogenetic 

 hypoblast with protochordal plate (pp.) and modified annular zone 

 (%. az.). 



In Figs. 92 and 93 the distinction between palingenetic and coeno- 

 genetic hypoblast is not actually existent, but arbitrarily introduced 

 in order to elucidate the facts as presented by 95. 



