178 



PRACTICAL PARASITOLOGY 



is very pronounced indeed in older, distended females, where the pro- 

 portion of the dorsal surface covered by the shield is very small. The 

 ventral surface presents other points of difference, being almost com- 

 pletely covered, in the male, with scales, which are separated from one 



another by lighter stripes. 

 In both sexes the ventral 

 surface bears two openings, 

 placed in the middle line. 

 In front is the transverse 

 genital opening, and behind 

 it, near the posterior margin, 

 is the anus. Upon each 

 lateral margin, just behind 

 the legs, is a rounded stigma 

 (peretreme), which appears 

 to be porous, and is sur- 

 rounded by a thickened edge. 

 In the centre of each stigma 

 is an opening, the spira- 

 culum, which communicates 

 with the tracheae. The stig- 

 mata of the male are oval, 

 those of the female circular. 

 The scales upon the ventral 

 surface of the male have a 

 certain specific significance. 

 Those in the median line are 

 the pregenital, genito-anal, 



and anal scales ; while the adanal and femoral scales are duplicated 

 upon either side. 1 



The finer structural details will be better seen in cleared specimens 

 and especially in macerated preparations of the chitinous skeleton. 

 The dorsal aspect of the capitulum differs 'in the two sexes. To right 

 and left, at the base of the female capitulum, is the so-called " porous 

 area," a circumscribed field with numerous pores, not to be mistaken 

 for eyes (Ixodes are eyeless). 2 The distribution of hairs and pores 

 upon the body surface and its appendages should be noted, and the 

 student should then pass on to the study of the legs. The legs are 



FIG, 89. Ixodes ricinus (L.). Male, seen from 

 the ventral surface. 21 : 1. (After a drawing by 

 A. Dampf.) 



1 The ventral surface of the female bears four longitudinal grooves, two of which 

 start near the vulva and run divergently backwards. The other two unite in a curve 

 in front of the anus, and the free ends also run backwards, either parallel to one 

 another or more or less divergent. 



2 In species with eyes, the eyes are always situated upon the scutum. 



