632 MR. J. WOOD-MASON ON THE FAMILY EMBIID^. [DcC. 18, 



or last of these sterna, in the same somite, that is to say, as that of 

 the male Cockroach, and one somite further back than in the female, 

 in which, as we have seen, it is placed between the eighth and ninth 

 sterna just as in female Cockroaches. All present a more or less 

 marked asymmetry of the caudal appendages ; and in some there 

 project between these appendages the tips of one or more " slender 

 spiniform processes," which Mr. M'Lachlan suggests may be an 

 intromitteut organ, but I consider to belong rather to a genital arma- 

 ture analogous to that of the common Cockroach. 



In Oligotoma saiivdersii, the only species of which I have as yet 

 examined spirit-specimens, the abdominal asymmetry is carried to 

 an extreme, and the genital armature is well developed and readily 

 seen. In this species not only are the caudal appendages unequal 

 on the two sides, but the tenth tergum and the ninth sternum also 

 depart widely from symmetry, especially the former, whicli, as will 

 be seen from the accompanying figures, is incompletely divided by a 

 deep angular notch into two unequal and greatly dissimilar parts ; 

 and each podical plate bears one or more processes forming an asym- 

 metrical apparatus of spines and hooks, which are analogous to the 

 incomparably more complex genital armature of most male Cock- 

 roaches, and doubtless serve, in the absence of an intromitteut organ, 

 to keep the aperture of the vas deferens closely applied to that of 

 the oviduct during copulation. 



On the Wrings. — No one can look upon an Embia without being 

 struck by the wide difference between it and such an insect as a fully 

 winged Cockroach in the mode and place of attachment of the wings 

 and in the condition of the wing-bearing somites. In the larvae of 

 all ametabolous insects the thoracic somites differ from those which 

 follow only in their greater size, and their terga are distinct from, 

 and overlap, each other just in the same manner as do those of the 

 abdomen ; they are, in fact, temporarily in the same condition they 

 permanently have in the Thysanura, which never possess wings — 

 young Blattce and young Earwigs resemblhig adult Campodea and 

 adult Machilis. The wings appear as expansions of the sides and 

 hinder angles of the two posterior of these somites, the terga of which 

 are in the perfect insect no longer freely movable upon one another, 

 but on the contrary are firmly knit together and soft, and have the 

 fully evolved wings attached to them along the whole length of their 

 sides. But species which have lost their organs of flight retain the 

 primitive characters of their wing-bearing somites throughout life. 



V\^e thus see that concentration of the two alary somites accom- 

 panied by flexibihty of their terga is correlated with the fully-winged 

 condition, and, conversely, that the absence of such concentration 

 and flexibility, that is to say, the retention of the primitive characters 

 of the thorax, is correlated with the wingless condition. 



In winged Embiidse, and especially in Oligotoma michaeli, the 

 thorax retains much of the primitive (larvalj character of its two 

 posterior somites, and the wings, instead of articulating with the 

 whole length, are attached along only very short portions, and those 

 at the extreme anterior ends, of the sides of their elongated somites. 



