METHOD OF DISSECTING TICKS 651 



larvae descended from a female tick which fed on a dog or cow only 

 slightly infected with P. cants or P. bigeminnm will be infected ; in 

 order to ensure success a large number of such larvae must be used in 

 order to infect the animal. 



2. In the case of transmission experiments with protozoal parasites 

 every precaution should be taken to exclude stray ticks from the experi- 

 mental animal. An animal should never be considered to be free from 

 ticks as the result of an external examination ; it should be isolated for at 

 least a week or ten days in order to allow the larvae and nymphs to drop 

 off. These stages are often difficult to find, especially when they bury 

 themselves among the hairs. Male ticks often remain attached for 

 months ; little or nothing is known as to what part they play in the 

 transmission of protozoal parasites. 



3. When conducting experiments with small animals, such as the dog, 

 in order to discover at what stage the infection is taken up and by which 

 stage it is transmitted, the larvae, nymphs and adults should be placed 

 with the animal and every one recovered when they become replete; 

 they should not be allowed to undergo metamorphosis in the cage and 

 then re-attach themselves to the animal. If this precaution is not taken 

 it will be impossible to be sure which stage carried the infection ; there 

 are numerous possibilities, some of which are noted in Chapter XII. ,: 



INTERNAL ANATOMY 



(PLATES LXXXIII, LXXXIV, LXXXV AND LXXXVI). 



There are several valuable papers on the internal anatomy of ticks ; 

 most of these, however, are of the nature of monographs, and do not 

 deal with the subject in a practical or indeed a simple manner. The 

 most satisfactory way of studying the parts is to learn first to recognize 

 them as they are exposed in a dissection, and this method will be adopted 

 in the following account. The method of dissection will be described 

 first. 



Partially fed females should be selected for dissection rather than 

 replete specimens, as in the case of the latter the diverticula, owing to 



the large quantity of blood which they contain, fre- 



J J . , Dissection 



quently rupture and may spoil the preparation. Alter 



some practice on partially fed specimens the manipulations can be carried 

 out rapidly, and even replete females can be dealt with. . The .dissecting 



