366 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



region of the head appears to be formed almost entirely 

 by the second maxilla? or labium. 



The thorax consists of three segments, viz., the 

 prothorax, the mesothorax and the metathorax (figs 1 

 and 3), the first being the smallest division of the three. 

 The three pairs of legs differ in no important features 

 from one another. Each leg is six- jointed and terminates 

 in a single claw, which, in the majority of individuals, is 

 armed with a small tooth on its inner margin (fig. 9). 

 Tarsi are absent in all Collembola, and, consequently, the 

 joint with which the claw articulates corresponds with 

 the tibia of other insects. 



The abdomen consists of six segments, the third 

 segment being greatly enlarged. On the ventral aspect 

 of the first segment is situated a prominent bilobed papilla 

 known as the ventral tube (y.t. in fig. 3). This organ is 

 the most characteristic of Collembolan structures, and it 

 varies a great deal in the degree of development to which 

 it attains in various genera. There arises from a point in 

 the mid-ventral line of the head a narrow furrow, which 

 is termed the ventral groove or linea ventralis (fig. •'>) ; 

 this groove is traceable backwards, passing between the 

 bases of the legs to the anterior aspect of the ventral tube, 

 where it terminates (Plate TV., fig 36). As will be 

 explained in a later chapter, the secretion of two pairs of 

 glands situated in the head flows down the ventral groove 

 and discharges over the surface of the ventral tube, which 

 it serves to moisten. The genital aperture is situated on 

 the ventral surface of the fifth abdominal segment near to 

 its posterior margin, and on the sixth and last segment is 

 situated the anus (fig. 3). The latter is surrounded by 

 three papillae, one of which is median and dorsal, and the 

 other two ventro-lateral. 



There is no sexual dimorphism among the Collembola, 



