280 ENTOMOLOGICAL SOCIETY 



during the larval stage and can be sometimes observed by a low 

 power of the microscope by transmitted light. Second, the now 

 fully developed respiratory system, externally the large saucer- 

 shaped stigmal plate behind and a little above the posterior pair 

 of legs, and the internal tracheal system ; third, the absence of 

 the genital orifices. The Ticks in this stage are still sexless. No 

 external character points to the future sex, and all nymphs, 

 whether they will hence be males or females, look alike, having 

 a dorsal shield. The body has become more firm than in the 

 larva, the mouth-parts and the legs have lost their hyaline aspect, 

 the chitinous sclerites which cover these parts have stronger de 

 velopment, the legs are now more slender and more cylindrical, 

 and the palpi and rostrum are darker in color, but are still 

 smaller than in the adult stage. The dorsal shield has not devel 

 oped to a larger size, and as the body has grown considerably 

 the shield appears proportionally much smaller than in the lar 

 val stage. 



When the Tick has moulted the second time, it passes into the 

 mature stage. Here the sexes are differentiated by prominent 

 morphological characters. 



The body of the mature Tick, male and female, in the free-living 

 state, is considerably flattened dorsally and somewhat less so on 

 the underside ; it is of an oval shape with slight variations in 

 some genera. 



In Ixodes it is somewhat constricted in the stigmal region, giv 

 ing the body a violin-shaped appearance ; in other instances the 

 one end of the body is more or less attenuated ; in Boophilus it is 

 the posterior part, in Dermacentor the anterior one ; while in 

 Amblyomma the body is more circular than oval. 



In the majority of genera of the Antistornata the families Ixo- 

 didse and Rhipistomidas the rounded anterior border of the body 

 is deeply excavated or squarely cut out, causing on each lateral 

 margin a sharp projection which affords protection to the capitu- 

 lum, inserted into the excavation. In the family Hasmalastoridas, 

 however, this excavation is wanting and the capitulum is here 

 connected with the body by a free pedicel, but, as I have been un 

 able to study specimens of this family, I cannot verify these state 

 ments. 



The body of the Tick is covered by a leathery integument, which 



