hearing on the origin of Insects. 157 



coalesced fellows of the opposite side by a fissure extending 

 to the apex of the triangular sternum ; finally, suppose 

 the integument of the limb-bases internally to the exopo- 

 dites to be pierced by apertures leading into glandular 

 pouches ; and we shall have arrived at an understanding of 

 the structure of the second abdominal sternum (fig. 3j in 

 Muchilis ; the second abdominal somite, in fact, closely 

 resembles the metathorax deprived of its five-jointed limbs. 

 The abdominal appendages of Machilis, therefore, are not 

 articulated to the sternum but to a sclerite, which repre- 

 sents the basal joints of a thoracic limb — to a protopodite, 

 in fact. In the somites anterior to the eighth the endo- 

 podites appear to be entirely absent, but in the eighth and 

 ninth of the female they are represented by the long, 

 jointed styles, two to each somite, constituting the four 

 elements of the ovipositor (figs. 6 and 8). 



In Lepisma, the appendages of the abdominal somites 

 anterior to the eighth are represented, as Lubl)ock cor- 

 rectly considers, by a group of stiff yellow setaj; internally 

 to these, on each side, is, according to the same author, 

 " a second similar group nearer the median line, Avhich 

 appears to represent a second process, formed by a pro- 

 longation of the ventral margin of the penultimate seg- 

 ment." It is clear that each of these more mesial pairs 

 of fringes are the remains, not of the prolongations 

 referred to, but of a pair of such rudimentary movable 

 endopodites as I find, in the male, attached to the upper 

 (dorsal) side, close to the inner margin of the prolonged 

 protojoodite (fig. 5) at about the same level as the longer 

 and indistinctly-segmented exopodites. These rudimentary 

 endojDodites are clearly homologous with the posterior 

 elements of the ovipositor in Mdcliilis and Lepisma. 



5§. When specimens of TlYac/izV/s maritima are plunged 

 into alcohol a single or a double pair of oval and peduncu- 

 lated bladder-like bodies is protruded, apparently, from 

 the posterior edge of the sternum, but, in reality, from the 

 apex of the coalesced basal joints of the limbs (imme- 

 diately internally to the rudimentary exopodites, Avhere 

 such are present) of each of the abdominal somites from 

 the first to the seventh, both inclusive. When first thrust 

 out they are as bright and, to the naked eye, as clear as 

 little globules of Canada-balsam, but they rapidly become 

 clouded and eventually opaque-white under the action of 

 the alcohol. The bladders are everted glandular pouches, 

 each ])rovided with a powerful retractor muscle, divided 



