ENEMIES OF APHIDES. 401 



sixty, seventy, or eighty joints. The segments are perfectly cyUn- 

 drical throughout, closely jointed, and, excepting the third, which 

 is longer, are of equal length Their appearance is that of a 

 round cord, divided at short intervals by transverse divisions. 

 They are covered with small hairs, laid evenly in the direction of 

 the axis, and I have never observed any deviation in this respect. 

 An antenna of Chiysopa, containing an unusually small number of 

 segments, but otherwise typical in structure, is shown on PI. XVIII., 

 Fig. 7. The antennae of the Coniopterygidoe are moniliform and 

 less hirsute than in Hemerobms. The number of joints is also less, 

 although it does not appear to have any definite relation to species. 



The Cocoon. 



The material from which the silky threads of the cocoon is 

 spun is derived from a gland situated in the posterior part of the 

 abdomen, and which opens by means of a short duct just within 

 the anal orifice. There appears to be no special organ for regulat- 

 ing the outlet, but the muscular bands connected with the sur- 

 rounding parts seem to control the duct, and probably when the 

 flow of silk-forming secretion is once established the larva has little 

 power of arresting it until the gland has completed its function. 

 Consequently, if a larva commences to spin on an unsuitable 

 surface — such as a glass cell — it does not stop after a few trials, 

 but goes on until it seems unable to make more silk, exhausting 

 its supply in making continual attachments to the glass in the 

 hope of obtaining a sufficient basis for the cocoon. The thread 

 itself, which is shown at Fig. 5, as spun on a cover-glass, is a fine 

 cylindrical cord of glutinous substance, which hardens imme- 

 diately. It is free from enlargements or irregularities of any kind, 

 and entirely devoid of any structure or duplication. It varies at 

 times in size, and is sufficiently adhesive as it leaves the larva to 

 broaden into a sticky mass, which is attached to convenient posi- 

 tions for the support of the pupa. 



The cocoon varies in shape and size, that of Chrysopa being 

 round or barrel-shaped and of a very dense texture ; that of 

 Hemerobius oval or egg-shaped, and consisting of comparatively 

 few fine and gauzy threads ; while in Coniopteryx the cocoon is 

 also oval, but is composed of dense spun silk. 



