THE GENUS DEMODEX 15 



fairly well developed in D. arvicolce and its varieties, being rather wide, 

 flattened dorso-ventrally, and sharply pointed ; there is a strong (often 

 salient) angle near the base (text-fig. 4 I). In B. cuniculi (possibly only 

 a variety of D. arvicolce) the spine is very similar to the one present in 

 that species, but reduced in size. This type of spine is also present in 

 I), erminece and 1). raiti ; in the latter, however, the spine is more 

 elongated and tlie angle near the base is rudimentary (not salient) (text- 

 fig. 4 H). There is no spine on the palp of 1). soricinus. The mouth- 

 parts apparently consist of two separate structures (text-figs. 2 & 3) : — 

 1 . The chelicerae apparently consist of a cylindrical basal portion and 

 two fingers or stylets, the dorsal stylet being quite short, but the 

 ventral one very long and fine ; the latter is often seen protruded, and 

 is called the maxillfe by most authors, but personally, I do not think 

 it is a separate structure. The proximal ends of the chelicerse seem 

 to be placed close beneath the triangular marking on the dorsal 

 surface, and slant obliquely till they reach the ventral surface, so that 

 the longer stylets lie almost ventrally. 2. Ventrally there is a pair 

 of tubes lying parallel with one another and forming the sheaths of 

 the chelicerse ; like the latter they can be protruded. Most authors arc 

 of opinion that these tubes are the chelicera?, but this certainly is not 

 the case. 



Leffs. — It is usually stated in works on Acari that the legs of tlie 

 Demodicidse consist of three segments only ; the great acarologist Beilese 

 declares, however (see ' Gli Insetti,' pp. 36 & 37, text-fig. 26), tiiat there 

 are five segments, and there can be no doubt as to the correctness of 

 his view. In well-mounted preparations of Demodex the five free 

 segments can easily be seen, the distal ones being usually angular and 

 rather salient on their inner surface. In addition to these there is also 

 the fixed basal segment (coxa or epimeron). Each leg ends in a pair 

 of claws which are provided with several minute denticles. (The 

 appendages of the immature stages of Demodex (I), muscardini) are 

 described in detail on page 31.) 



Mespiratory system.- — A pair of very minute openings are present on 

 the ventral surface of the capitulum, near the base. These apertures 

 were noticed by Csokor, who regarded them as the openings of glands. 

 It is more probable, however, that they are the orifices of the respiratory 

 system. A short tube seems to lead internally from each opening, 

 soon uniting with that of the opposite side to form a central ring- 

 like structure ; apparently after this the tracheae diverge again to form 

 one or more main lateral trunks, giving off smaller branches to the 



