THE GENUS DEMODEX. 31 



times as long as wide. Capitulum+cephalothorax about as long as the 

 abdomen. Genital opening situated further back on the dorsal surface 

 than is usually the case in the genus, being placed above the transverse 

 groove between the second and third pairs of legs. Penis short but 

 slender. 



Dexitonymphs. — The older nymphs are elongated, and the posterior 

 end of the abdomen is usually pointed. Their capitulum is shorter and 

 narrower than is the case in the protonymphs. The proportions of the 

 body vary very much, according to size and degree of development. In 

 small specimens the body is from 3-4 1 times as long as the greatest 

 width. A larger specimen of this stage (containing an almost fully 

 developed specimen of the final or adult stage) has the abdomen a 

 little longer than the cephalothorax+capituliim, and the total length is 

 slightly more than four times the width. Appendages of deutonymph 

 rather similar to those of the protonymph, but more leg-like in 

 structure, for several segments can be distinguished ; two clusters of 

 denticles are present on these appendages. The four pairs of semi- 

 circular structures on the ventral surface are present, but much smaller 

 than in the protonymph. 



Protonymphs. — The nymphs of I), muscardini differ from the adults, 

 not only in shape, but also in important details of structure. The 

 earlier nyraphal stage (protonymph) is rather short and wide, the total 

 length of the body being only from slightly more than twice up to a 

 little less than 2| times as long as the greatest width; posterior end of 

 the body rounded off. Capitulum of this nymph very short and wide, 

 being twice as wide as long. True legs are not present, being replaced 

 by very short appendages, which chiefly consist of a chitinous plate or 

 epimeron. The inner end of the epimeron is angular, terminating in a 

 sharp point, whilst the outer end is rounded off. Each of the eight 

 epiraera boars two tiny but distinct tubercles on its surface; these 

 tubercles being of equal size and furnished with 3-4 minute but distinct 

 denticles ; (fig. 32 is a lateral view of a very young nymph 72 |M, in length, 

 showing the position of the tubercles on the epimera). Four pairs of 

 curious epidermal structures are also present nearer the middle of the 

 ventral surface of the body. They are semicircular in shape, the 

 posterior margin is curved and furnished with sharp denticles, 5-6 in 

 number in the case of the anterior ones, but the last has only four 

 denticles. These semicircular discs could easily be mistaken for the 

 developing legs of the next stage, but are not internal in position, but 

 quite superficial, being placed on the ventral surface of the body. 



