202 OETHOPTERA. 



the anus (Tab. XI. fig. 10, a)*. The four appendages, notwithstanding their resem- 

 blance, are thus proved to be of quite a different nature. 



All the Tridactylinae seem to have fossorial habits. They live in the sandy beds of 

 rivers, and run and jump with great agility on the surface of the water. When 

 submerged by the whirling of the current, they hop with the utmost vigour in their 

 endeavours to reach the surface, and when that is gained they make tremendous leaps 

 to reach the shore f . « 



The aquatic habits of these interesting little insects explain, perhaps, the use of their 

 four anal appendages. When submerged, they carry with them little bubbles of air, 

 between the hind femora and the abdomen, which perhaps enable them to breathe 

 under the water, and, acting like bladders, bring them again to the surface. It is 

 probable, too, that bubbles of air are also retained between the four pubescent anal 

 appendages ; but I have not succeeded in verifying this with sufficient certainty, on 

 account of the rapid movements of the insects. 



The affinities of the two genera composing the group Tridactylinae are not the same, 

 and it is surprising that two types so similar to each other incline towards two different 

 families : Tridactylus being more allied to the Gryllotalpinae, having no ovipositor 

 whatever ; while Bhipipteryx inclines towards the Acridiidae, as will be seen below. 



TRIDACTYLUS, Oliv. 



Tridactylus, Olivier (1779).—Heteropus, Palis.-Beauv. (1805).— Xya, Illiger (1835). 



Feminse ovipositore destitutae. — Abdomen sicut in Gryllotalpis, in utroque sexu conforme ; segmenta dorsalia 

 10, ventralia 8 obferens. Cerci biarticulati, articulo secundo brevi ac gracili, mobili. Appendices anales 

 inferi cylindrici, indivisi. 



These small insects are closely allied to Gryllotalpa. The body is similarly formed ; 

 the head is conical, directed forwards, well suited for progression underground ; the 

 anterior tibiae are strongly fossorial, and are used for digging galleries in the sandy 

 shores of rivers, instead of in the fields, as in Gryllotalpa J. The females have 

 no ovipositor whatever, and the abdomen has consequently the same number of 

 segments in both sexes. This is the reason why the males had never been properly 

 distinguished from the females. 



There is, however, a difference to be noticed between the sexes : in the females of 

 T. variegatus the penultimate ventral segment has generally a slight notch in the 

 middle of the hind margin (Tab. XI. fig. 6), and it is followed by a sort of appendage 



* Vide Saussure & Zehntner, Notice morphologique etc. p. 410. 



f For the aquatic habits of the Tridactyli, vide H. de Saussure, Miss. Scient. Mex., Orthopt. p. 322. 

 t Their habits have been described in a very charming way by L. Dufour and by Foudras. (Extract in 

 Serville, Orthopteres, p. 313.) 



