INVERTEBRATAj CRYPTOGAMIA, MICROSCOPY, ETC. 65 



shown by Sir J. Lubbock, an ftppendago articulated to the suture which 

 constricts the coxa, on the upper side of the leg ; in Lepisma and 

 Blatta the coxa is two-jointed and articulates with a basal joint ; so 

 the accessory appendage in Machilis represents an exoj^odite articu- 

 lated to a three-jointed protopodite, the condition shown by the 

 crustacean Penem, &c. 



In the Myriapod Scolopendrella almost all the legs possess an 

 appendage similar to the previous one, on the inner side of the first 

 free basal joint, apparently reiDresenting an endopodite ; this neces- 

 sitates the leg itself being regarded as an exopodite, whereas that of 

 insects must be an endopodite. 



The movable opjyendages of the abdominal sterna in Macldlis are 

 articulated to an intervening sclerite — which is probably the condensed 

 protopodite — and represent exopodites, the endopodites of the series 

 appearing only in the four styles of the ovipositor. In Lepisma a 

 more median series of setae in the anterior abdominal segments 

 probably constitutes the endopodites which correspond to the exopo- 

 dites formed by the more lateral series of setaB. 



Within the apex of the basal joint of the first seven abdominal 

 limbs in Machilis lie some glandular pouches, in varying numbers ; 

 they occur also in Nicoletia and Campodea, and probably represent 

 segmental organs, for the probable openings of these organs in Peri- 

 patus are similarly placed. They appear to be represented in the 

 Collembola by the median ventral sucker ; for this shows traces of 

 being originally double, in the median slit of Podura and Lepisma, 

 and in its bifurcation in Orchesella, the Smynthuridce and Papiriidcp.. 

 Their ajijjarent absence in the generative segment may be due to their 

 conversion into genital or accessory genital apertures and ducts. 

 The sti/les of the ninth abdominal segment of male Blattidce appa- 

 rently represent the external abdominal appendages of the Thysanura ; 

 in one si)ecies the female carries a double appendage on the eighth 

 segment, and on the ninth the styles which correspond to the male 

 styles, while beneath is a flattened pair of organs corresponding in 

 their position, and probably in their morphological significance, to 

 the long setose appendages of the ovipositor of Machilis. 



Direction of the Flight of Insects.* — The difference in the flight 

 of birds and insects has been shown by M. Marey to consist in tho 

 power possessed by the former of modifying the angle at which tlio 

 wing vibrates, and so changing the directicm of flight ; whilst insects, 

 with a few exceptions, are deprived of this power, tho muscles not 

 being attached to the wing but to the portion of the thorax that 

 sujiports it. 



After numerous experiments on insects of all orders, M. Jousset 

 de Bellesme concludes tliat the direction of the flight of insects is 

 determined by the position of the head and thorax, tliis position 

 depending on the respective positions of the centre of gravity and the 

 axis of suspension. These two elements are sometimes both movable ; 

 more frequently, however, it is the centre of gravity alone that is 

 displaced. 



* ' Coniptes Eoudus,' Ixxxix. (1879) p. 980. 



vol-. III. F 



