OVIPOSITOR OF ACHORUTES. 139 



supplementary tooth, as in Achorutes (Fig. 172, c). This spring 

 is in part homologous with the ovipositor of the higher insects, 

 which originally consists of three pairs of tubercles, each pair 

 arising apparently from the seventh, eighth, and ninth (the lat- 

 ter the penultimate) segments of the abdomen in the Hymenop- 

 tera. The spring of the Podura seems to be the homologue of 

 the third pair of these tubercles, and is inserted on the penulti- 

 mate segment. This comparison I have been able to make from 

 a study of the embryology of Isotoma. 



Another organ, and one which, so far as I am aware, has been 

 overlooked by previous observers, I am disposed to consider as 

 possibly an ovipositor. In the genus Achorutes, it may be found 

 in the segment just before the spring-bearing segment, and 

 situated on the median line of the body. It consists (Fig. 163) 

 of two squarish valves, from between which 

 projects a pair of minute tubercles, or blades, 

 with four rounded teeth on the under side* 

 This pair of infinitesimal saws reminds one of 

 the blades of the saw-fly, and I am at a loss 

 what their use can be unless to cut and pierce 

 so as to scoop out a shallow place in which to 

 deposit an egg. It is homologous in situation 

 with the middle pair of blades which composes 

 the ovipositor of higher insects, and if it should 

 prove to be used by the creature in laying its lesTcatchliolding 

 eggs, we should then have, with the spring, an spring of Acho- 

 additional point of resemblance to the Neurop- 

 tera and higher insects, and instead of this spring being an 

 important differential character, separating the Thysauura from 

 other insects, it binds them still closer, though still differ- 

 ing greatly in representing only a part of the ovipositor of the 

 higher insects. (This is a catch for holding the spring in place.) 



But all the Poduras differ from other insects in possessing a 

 remarkable organ situated on the basal segment of the abdo- 

 men. It is a small tubercle, with chitinous walls, forming two 

 valves from between which is forced out a fleshy sucker, or, as 

 in Smynthurus, a pair of long tubes, which are capable of being 

 darted out on each side of the body, enabling the insect to 

 attach itself to smooth surfaces, and rest in an inverted position. 



The eggs are laid few in number, either singly or several 

 together, on the under side of stones, chips or, as in the case 



