338 



The dimensions of the various stages of 

 /. ricinus are : — 



Eggs ... o"4 by o'3 millimetres. 



Larva .. o"6 by o'4 millimetres. 



Nymph ... 1-3 by o'6-2 millimetres. 



Adult 2'5 by I '5 (male) millimetres. 



Adult io-iiby6-7 (female full 



grown) millimetres. 



Ticks have a predilection for certain hosts, 



but the same tick may be found on different 



animals, and, further, the larval and adult stages 



may be passed on different animals. 



External Anatomy 



Technique. — Collect ticks from the ears of dogs, bellies of 

 cattle, sheep, etc. Preserve in spirit. Make out in fresh speci- 

 mens the following points, dissecting, if riecessary : — 



1. The Rostrum, capitulum or head, is the 

 small anterior projecting portion, it is joined on 

 by a short neck to the scutum ; on its ventral sur- 

 face is seen — 



2. The Labium or hypostome, a bi-laterally 

 symmetrical structure, furnished with a number of 

 teeth directed backwards. The number of rows 

 of teeth and their disposition are very important 

 in classification. 



3. The Mandibles lie dorsally to the labium. ' 

 The terminal portion (digit) terminates in two 

 or three processes, apophyses, which bear hooked 

 teetli directed backwards. They are important 

 in classification. 



4. The Mandibular Sheath lies above the 

 mandibles. The anterior extremity is notched 

 corresponding to the two halves of the sheath. 



