HATCHING OF STEMOPSOCi'S CRUCIATUS 6i 



OBSERVATIONS ON THE HATCHING OF 



STENOPSOCUS CRUCIATUS. 



By (Miss) L. H. HuiE, F.E.S. 

 (Plate I.) 



Among the many adaptive structures of insect anatomy, 

 " hatching spines " are not the least interesting. These 

 temporary structures for breaking the egg-shell have been 

 described in several cases. Packard in his Textbook of 

 Entomology cites five such , instances, while three others are 

 mentioned by P. de Peyerimhoff in a paper to w^hich I shall 

 again refer. Amongst other Arthropods similar structures 

 are known, varying in form, from a simple tooth to a file or 

 sawlike implement. 



The eggs of the Psocid Stenopsocus cniciatus are laid on 

 the under side of holly leaves in clusters of six to twenty or 

 so. They are fixed to the leaf by a gummy substance, and 

 further fastened on, and to each other, by a slight webbing. 

 Laid in the late summer, they hatch in the following spring. 

 They are oval in shape, and measure less than half a 

 millimetre in length. At first they are white, but as they 

 ripen they become brown and exhibit at one end a little 

 black stripe. The presence of this peculiar mark led me to 

 pay attention to the eggs, and examine them microscopically. 

 The egg-shell is very transparent, and in a ripe ^^'g the 

 embryo appears as shown in Fig. 3, which represents the 

 ventral aspect. The back of the head and thorax are 

 towards the under side of the egg, and the abdomen is 

 doubled up in front. On each side of the bulging clypeus 

 are seen the 8-jointed antennae, and the palps and folded legs 

 fill up the oval. But the most conspicuous object of all is the 

 dark-coloured egg-breaker, the origin of the short black mark 

 I have mentioned. It is a comblike file or saw (Figs, i, 3, 

 4) borne vertically on the head, and received at its upper 

 extremity into a notch in the fore part of the epicranium. 

 The lower end of the file indents the centre of the still soft 

 clypeus, through which is often traceable a converging 



