42 



researches of AVilleiii go to prove that in the g-reater 

 numbe]' of Collembola (i.e., in the SminthuricUe, the 

 Eutomobryidse and in some of the Aehorutidsej the eyes 

 are constrncted on the eucone principle, and he regards 

 them as being incipient compound e^'es. In several 

 genera of the Achorutidse (including Anurida) he points 

 out that there is no layer for the secretion of a crystalline 

 cone, and hence he looks upon the eyes of such forms as 

 being ocelli or stemmata. He remarks (27 p. 90): — 

 " La consideration que les ocelles s'observent parmi les 

 Podurides, chez des formes animals oii les orgranes visuels 

 sont manifestement regression, incite a admettre que ces 

 stemmates sont productions derivees de I'ommatidie 

 eucone par la disparition du systeme lentigene, con- 

 clusion qui accords avec des faits observes par Patten 

 dans le developpement des ocelles de Yespa et de larve 

 ^VAcilms, et qui autorisent a admettre que les stemmates 

 a deux couches cellulaires de ces Insectes derivent d'un 

 oeil a trois conches (comme I'ommatidie euconej par 

 I'atrophie on le developpement incomplet de la strate 

 moyeune." 



If the extreme simplicity of the structure of the 

 eves of Anurida is due to retrogression, and is not a 

 primitive character, it lends support to a belief 

 maintained by certain students of the Collembola, viz., that 

 ATniridd is, in some respects, a degenerate type. 



The post-antennal organ (Plate I., figs. 4, 5 and 10, 

 Plate III., fig. .j4) is a curious cuticular structure, circular 

 in form and situated one on each side of the head 

 immediately in front of each protuberance which bears 

 the ocelli. It consists of a variable number of somewhat 

 triangular bodies, which are in close contact with one 

 another, with their apices directed towards its centre. 

 The number of these bodies varies in different individuals, 



