

INTERNAL ANATOMY. 119 



(an exceptional Gamasid),* Winckler's paper, also on 

 Gramasida3,t von Schaub's on Hydrodroma (Hydro- 

 phantes), one of the Hydrachnidse, { and a certain 

 amount in Henkin's paper on Trombidiwn. 



The muscles of the Acarina are usually most dis- 

 tinctly striped ; this, however, is not, perhaps, quite as 

 conspicuous in the Tyroglyphidse as in most of the 

 higher groups ; still it is almost always striped muscle 

 that is found. Nalepa remarks that the striping is not 

 equally conspicuous in all the muscles, and is difficult 

 to see in some of those which shorten the body lon- 

 gitudinally, while it is very striking in others, e. g. 

 the genital muscles of the 3 . The sarcolemma may 

 usually be traced without special difficulty ; but the 

 nuclei on the muscles are usually few and not very 

 easily seen. Nalepa says that the section of the 

 muscles in the Tyroglyphida3 is generally round or 

 prismatic, seldom flat; he is doubtless right on the 

 whole ; although it seems to me that flattish muscle- 

 bands are not by any means rare. As in most families 

 of Acarina, a large proportion of the muscles of the 

 Tyroglyphidse are inserted into the parts they move 

 by means of tendons, which are sometimes short but 

 often very long and occasionally assume considerable 

 importance. The muscles usually diminish gradually 

 in thickness from their point of origin to that of 

 insertion. 



The principal groups of muscles in the Tyroglyphidse 

 may be considered to be 



1. The muscles of the rostrum and mandibles. 



2. The dorso- ventral muscles. 



3. The muscles which shorten the body. 



* " Ueber Halarachne Halichoeri, Allrn.," in ' Zeit. Naturw.,' Bd. 

 Iviii (1885). 



f " Anatomie der Gamasiden," in ' Arb. Inst. Wien,' 1888, Bd. vii, 

 Heft 3, pp. 317354. 



J " Ueber die Anatomie von Hydrodroma" in ' Sitzb. Ak. Wien,' 

 Bd. xcvii (1888), pp. 98151. 



" Beitrage zur Anatomie, Entwicklungsgeschichte und Biologic von 

 Trombidium fuliginosum," in ' Zeit. wiss. Zool.,' Bd. xxxvii (1883), pp. 

 555, 663. 



