TYPE OF DEVELOPMENT OF ARTICULATA. 53 
rounded itself with a germinal membrane, a portion of it 
thickens into a long germinal stria, resembling an elon- 
gated ellipse. This is the rudiment of the ventral side of 
the futureanimal. A groove then divides it into the two 
germinal laminz, and transverse stria next make their 
appearance, the indications of the so-called primordial 
segments. The symmetrical disposition of the organs, 
and the integration of the body out 
of consecutive segments, is herewith 
initiated. All further development 
emanates from these primordial seg- 
ments, which are the standard of the 
Annelids or higher Vermes; while in 
the Articulata, projections and ap- 
pendages of these segments develop 
into feelers, manducatory apparatus 
and legs, and by their heterogeneous 
integration in the regions of the 
head, and of the middle and posterior 
portions of the body, give rise to the 
vast variety within the type. In each 
particular case we see what is special Fic. 6 
emanate from what is more homogeneous and undiffer- 
entiated, and this is likewise corroborated by the more 
advanced phase portrayed in the diagram (fig. 6). It 
represents the embryo of the great black-beetle (Hydro- 
philus piceus) on its ventral side. The antenne (/), the 
three pair of oral appendages (#z), and the three pair of 
legs, are as yet little distinguished. In the further course 
of development, the lateral portions grow towards the 
back, in the centre of which they finally meet. <As 
compared with the Vertebrata, it may hence be said 
