282 ME. A. D. MICHAEL ON THE VARIATIONS IN THE 



stood. The same remarks apply to the Plates ; for although many organs are necessarily 

 drawn, particularly in the sections, as to which I have little or nothing new to say, yet 

 it is only in order to show their relation, or position relatively, to those which are new or 

 Avhich do vary from known forms. It will, I hope, be found that there is not any 

 drawing which does not contain something not hitherto known or figured. 



The GamasinEe are the typical subfamily of the Gamasidse, the other subfamiUcs being 

 the Uropodina?, the DermanyssinsB, and the Pteroptinse ; the two latter subfamilies are 

 wholly parasitic, and their anatomy, so far as it is at present known, is, as might be 

 expected, not so highly developed as that of the other two subfamilies. The Uropodina? 

 diflTer considerably in internal organization from the greater part of the Gamasinse, and 

 their internal anatomy has been dealt with by myself and others, as mentioned below. 



Meo"nin has claimed that the Gamasinse are the most highly organized of all the 

 Acarina ; and although they are devoid of eyes, which are possessed by several other 

 families, the great development of the so-called brain — i. e. the circumo^sophageal 

 o-anglion, for such it is, all commissures being lost in one mass — the elaboration of the 

 trophi and muscular system, the existence of a heart or dorsal vessel, &c. probably 

 entitle them to that position. They are mostly very active creatures, having fully 

 chitinized dorsal shields and legs, and a ventral surface either entirely or partially 

 covered by chitinized plates, the arrangement and form of which is often characteristic 

 of species or of genera. 



It used to be supposed that the Gamasinai fed upon vegetable matter in process of 

 decay. In the year 1880, however, when investigating the life-histories of some of the 

 species for the purposes of a paper in the ' Journal ' of this Society, I found, as there 

 stated, that they would not live in my cells on vegetable matter, but that they throve 

 admirably on a diet of live cheese-mites (Tyroglyphidse), and since then I have had 

 frequent opportunities of observing the predatory nature of many of the species. I 

 believe also that Col. Blathwayt, of Bath, who had also been unsuccessful in rearing 

 Gamasinse upon a vegetable diet, has been perfectly successful over a considerable period 

 since he has adopted the mode of feeding suggested in that paper ; he also uses small 

 insects *. Some of the species apparently feed upon small dead insects and other 

 creatures. 



A general idea exists that the Gamasina? are parasitic. This, however, is not by any 

 means universally the case ; the greater number of species are free-living, and not para- 

 sitic in any stage ; some are parasitic in immature stages, but not in the adult. The 

 adult male is very rarely parasitic, and where parasitism exists, even in the young, it is 

 often very doubtful whether they require anything from their hosts beyond conveyance. 

 The presence of some amount of moisture in the atmosphere and surroundings is 

 essential to the existence of most, if not all, of the species. 



BiBLIOGUAPHY. 



The anatomy of the Gamasinse is not by any means a new subject. The memoirs 

 regarding it are few, but some of them are very good. 



* " On some common Hpocies of Gamasidie," Journal of Microsc. and Nat. Sci. u. s. vol. ii. (1889) p. 102. 



