2 Pi-oceedings of the Roi/al Irish Academi/. 



of the specimens come from the granite islands of the Seychelles Archipelago 

 in the restricted sense ; most are from the forest-clad, mountainous islands of 

 Mahe and .Silhouette, a much smaller number from the islands of Felicite and 

 Praslin. Collections of Apterygota were also made on Coetivy to the south 

 and on some of the coral islands to the south-west of the true Seychelles 

 group — the Amirante and Farquhar, and Aldabra — the latter of which lie 

 noith-west of Madagascar. A discussion on the geographical bearing of the 

 facts of distribution of the insects is given at the end of tliis paper 

 (pp. 48-55) . 



The Apterygota are now generally recognized as a sub-class of the Insecta, 

 showing a number of interesting primitive characters which afford a strong 

 pi'esumption in favour of the view that their universally wingless condition 

 is to be regarded as a survival inherited from the remote ancestors of insects, 

 and not as an adaptation to some abnormal mode of life like the pai-asitism 

 of such insects as lice and fleas, whose winglessness is clearly a secondary 

 character. On account of tlieir inability to fly, and the wide and often 

 discontinuous range of many genera and species compared with the curiously 

 restricted distribution of others, the Apterygota may be regarded as specially 

 important in faunistic studies whicli open up problems of ancient geography. 

 The rich collections of these insects which have been gathered in the Seychelles 

 and neighbouring archipelagoes promise, therefore, results of some importance. 

 The two main orders of Apterygota which were recognized by Lubbock in 

 his classical monograph (73), the starting-point for most English-speaking 

 students of the group, are both well represented iu the collections now 

 described. These orders can be readily distinguished by superficial 

 characters : — 



A. Feelers long, multiartieulatc. Ten abdominal segments. Often 



eight pairs of simple abdominal appendages, . . Tkysanura. 



B. Feelers with four to six segments. Abdominal segments six 



only. At most three pairs of abdominal appendages, reduced 



or modified, C'ollembola. 



Order THYSANUEA. 

 The Thysanura or " Bristle-tails " are well represented in tlie fauna of the 

 Seychelles. Hitherto only two species of the order — Acrotelsa collaris (Fab.) 

 and Le]}idospora Bmueri Esch. — appear to have been recorded from the 

 archipelago ; both of these belong to the extensive family of the Lepismidae. 

 In the collection now described, eight species (four of them new) of this 

 family are enumerated, besides three of the Machilidae, and one each of the 

 Campodeidae and the lapygidae — all of these being apparently new. Thus 

 the four princii:>al faruilies of the Thysanura have members among the insect? 



