26 ARKIV FÖR ZOOLOGI. BAND 3. N:0 28. 



The shape is characterized through the width being as 

 great or even greater than the length, and through the flatness. 

 A rounded broad shape very often occurs in ectoparasitic and 

 commensualistic Acari as for instance in Disparipes, Imparipes, 

 many Uropodmce. Antennophorus, Myrmonyssus and others 

 but in Neomegistus it may be said to reach its maximum. Ber- 

 LESE in his great work upon the myrmecophilous acari calls 

 attention to this pecuHar shape, which he calls facies antenno- 

 for oide, but he does not discuss the question, why it is of greater 

 advantage to the mites than the usual shape, or how they ha ve 

 acquired it. He only says »Questa facies deve corrispondere 

 alla piii opportuna dispositizione del corpo e degli organi per 

 un dato abito, come pruö essere quello di starsene in atto e modo 

 speciale sulle formiche (o su altri artropodi)». 



The following observation which I made on the manner of 

 locomotion of the present forms, seems to throw some light 

 upon this question. It appears from this that they are able 

 to move with the same agility backwards and sideways as for- 

 wards or even better sideways; at least they were most fre- 

 quently seen moving sideways. That the ability to move in 

 different directions without turning round offers great ad van- 

 tages to the mites goes without saying. And at the same time, 

 as the sagittal axle has ceased to lie in the line along which 

 the animal chiefly moves, the reason why this axle should be 

 longer than the other has ceased to exist. As a rule the lon- 

 gest axle of an animal is coincident with the line along which 

 the animal is moving, as for instance in those crabs, which 

 always run sideways, the träns versal axle is longer than the 

 sagittal. In Paramegistus both axles are of the same length, 

 in Neofnegistus the träns ver sal one is even slightly longer. 



The hairs of the body also show special adaptations. On the 

 dorsal shield they are practically missing, as far as that they 

 are exceedingly minute and hyalin, but their pores are very 

 large and besides these there are especially in Paramegistus 

 other numerous pores, and the hypodermic cells are very large. 

 Very likely they emit some f luid which renders the cuticle slip- 

 pery. The mites were as a matter of f act shining and polished. 



On the marginal shield in Neomegistus (and in Echinome- 

 gistus) the hairs are modified into strong spines which un- 

 doubtly in some way increase the animaFs power of adhering to 

 the Julidse, as other, ectoparasitic acari, the genera Imparipes, 



