46 ON THE ORIGIN AND [CHAP. 



Kolliker himself, however, frankly admits that " meas 

 de hoc insecto observationes satis sunt manca," and 

 it is possible that he may never have met with an 

 embryo in the state immediately preceding the ap- 

 pearance of the legs ; especially as it appears from 

 the observations of Kowalevski that in Hydrophilus 

 the appendages do not make their appearance until 

 after the segments. 1 



On the whole, as far as we can judge from the 

 observations as yet recorded, it seems that in Homo- 

 morphous insects the ventral wall is developed and 

 divided into segments, before the appearance of the 

 legs ; but that the latter are formed almost simul- 

 taneously with the cephalic appendages, and before 

 either the dorsal walls of the body or the internal 

 organs. 



As it is interesting, from this point of view, to 

 compare the development of other Articulata with 

 that of insects, I give a figure (Fig. 32), representing 



* 



FIG. 32. Egg of Pholcus opilionides (after Claparede). 



an early stage in the development of a spider 

 (Pholcus) after Claparede, 2 who says, " C'est a ce 



1 Mem. de 1' Acad. Imp. des Sci. de St Petersbourg. tome xvi. 1871, 

 p. 35. 2 Recherclies sur 1'Evolution des Araignees. 



