32 BRITISH TYROGLYPHIDyfl. 



Oudemanns,* who proposes the terms " prosoma "and 

 " metasoma," instead of cephalothorax and abdomen t 

 in the case of the Acari. It is not, however, apparent 

 to me why the legless condition should be considered 

 essential. It will not be denied that in many Arthro- 

 poda the abdominal segments, or some of them, bear 

 appendages of some sort, v.g. the swimmerets of the 

 Macrura, the pleopods of the Isopoda. etc. It does not 

 appear to require any great stretch of imagination to 

 suppose that some of these may become functional as 

 locomotive limbs in some Arachnida, but it is said that 

 the Spiders, Scorpions, etc., are without such legs. 

 This is true, but it must be remembered that the Acari 

 probably form the great bulk of the Arachnida, being, 

 as far as we can judge at present, much more numerous, 

 both in number of species and in number of individuals, 

 than all the remainder put together ; and although some 

 biologists are inclined to regard them as degraded forms, 

 yet there are many indications pointing rather to their 

 being a primitive group. At all events, what is called 

 the abdomen in the Acarina functions as such, and con- 

 tains the internal organs which we find in the legless 

 abdomina of allied creatures ; and in many cases (e.g. 

 Oribatidse) it is divided from the cephalothorax by a 

 phragma, through which the alimentary and nervous 

 systems pass. 



I do not like the expression " Acarina " for a portion 

 of the Mites, because it has always been considered to 

 include the whole. 



I do not see that the trachea of the Prostigmata can 

 be said to be " atrophied in the aquatic types ; " it 

 should rather be said in some of the aquatic types ; in 

 the Hydrachnidge the trachea are very fully and well 

 developed. I, however, quite approve of retaining the 

 Halacaridae among the Prostigmata, in spite of the 



* "List of Dutch Acari," in ' Tijdsohr. Ent.,' Deel xxxix (1896), p. 64. 

 f "Notes on Acari," in 'Tijdschr. Ent./ Deel xxxix (1896), pp. 175 

 187. 



