Tivo Tijpes of Trachew in Ardchn'ula 133 



situated in tlie soft lateral part of the body, consequently higher than the coxaj of the limbs ; 

 and the case of those Acari (Prostigmata Kramer) whose spiracles are placed close together 

 above the bases of the autennai (mandibles of most writers), has not been present to the mind 

 of McLeod on this occasion. The four pairs of spiracles in Notostigmata are all dorsal (With). 



Whilst the difference between Ricinulei and Pedipalpi in regard to the position of the 

 spiracles appears to us essential, we do not consider that the difference between them in 

 respect of the respiratory organs is of any great weight. In uur opinion the respiratory 

 organs in Arachnida belong to two tlifferent types. One of these is found in Solifugie (see 

 Kittarv, pp. 34o — 353), Opiliones, and, amongst Acari, in Ixodiiite and Notostigmata, viz. richly- 

 ramitied trachea?, with distinct spiral thickening. The other type occurs in Chelonethi (see 

 Croneberg, pp. 445, 446), Ricinulei, Araneaj, and apparently in the majority of Acari tracheati\ 

 viz. trachea? of which the thickenings are not spiral but linear annular, or replaced by mere 

 thicker points, and which are either slightly or not at all ramified, or else in bundles from 

 the trunks. We agree with Leuckart and several other writers' in looking upon the so-called 

 lungs in Scorpions, Pedipalpi and Araneae as mere modifications of the trachese of the second 

 type. Apart from the order of Acari, which in so many resjjects exhibit so much variety, it 

 must be admitted that the two kinds of tracheae which we look upon as constituting the two 

 types, do not occur within the same order or in nearly allied orders of Arachnida, but slightly 

 ramified or tuft-shaped trachea? of the second type are found in nearly allied orders, or even 

 within one and the same order, and the difference in this respect is consequently of less 

 importance. Within the limits of Aranese it is well known that Aranese theraphosa? Sim. and 

 Hypochilus have (see Simon e, pp. 6, 7) two pairs of so-called lungs, whilst the other Ai-aueae 

 vera? have one pair of lungs aud one pair of tuft-shaped or slightly ramified tracheae (according 

 to Bertkau). According to an investigation by Bertkau, first published very briefly by Thorell, 

 and later on at greater length by Simon (e, Vol. i. pp. 326, 327), the family Caponiidae, com- 

 prising the genera Nops MacLeay, Caponia E. S., and Capunina E. S., shows a very interesting 

 exception to this rule. The figures of Bertkau, published by Simon, enable the reader to form 

 a good judgment on the structure in question. A strong trachea showing some few ramifi- 

 cations originates from the second pair of spiracles ; from the first pair of spiracles arise a 

 pair of respiratory organs which, in Simon's own words, are " des trachees qui consistent en 

 un tronc principal, court, qui donne naissance a des fines ramifications en forme de buissons." 

 We may add that this first pair of respiratory organs in Caponiidae presents a considerable 

 resemblance to the single paii' of organs in Ricinulei, yet with the difference that the stem 

 from which the tracheal tubes originate is much larger in Ricinulei than in Caponiidae. The 

 fact that Ricinulei and Caponiidae possess only tracheae, whilst Thelyphonoidae, Amblypygi, 

 Araneae theraphosa? and Hypochilus have only lungs, but the great majority of Aranea? 

 possesses both forms of organs, proves therefore that no great weight can be attributed to 

 this difference. 



1 According to the statements of authors whose investiga- the so-called lungs in Araneee (Lycosa) have at first the 



tions must be looked upon as fully trustworthy, such is at any appearance of long, slightly-ramified tracheae, of which the 



rate the case in OribatidiE (Michael, a, pp. 168 — 176), Bdellidse terminal portion disappears at a later stage of development, 



(Michael c, pp. 518, 519 ; PI. xlhi. fig. 45), Trumhidium whilst the pulmonary leaves are developed in the basal por- 



(Henking, p. 565, PI. xxxiv. fig. 7). In the last-mentioned tion of the trachea;, for which reason he shares the view of 



case the absence of the spiral thickenings is, however, not Leuckart. While not omitting to mention this, we do not 



specially mentioned. We have ourselves examined the feel justified in attributing great weight to this observation, 



tracheae in Ixodes. which, as far as we are aware, has not been corroborated by 



- According to the investigations of Jaworowsky (p. 65) other observers. 



