376 TEXT-BOOK OF ENTOMOLOGY 



distance of nearly an inch from each side of the neck. While exam- 

 ining the very gayly-colored and heavily-spined caterpillars of Schi- 

 zura concinna we observed that when a fully-grown one was roughly 

 seized with the forceps or fingers it sent out a shower of spray from 

 each side of the prothoracic segment, exactly like that of Cemra 

 and Macrurocampa. 



In the European Centra vinula the apparatus consists of a single 

 sac, which opens by a narrow transverse slit on the under side of 

 the neck, out of which is rapidly everted four lateral tubes, two 

 on each side (Fig. 366, 4, t), which are withdrawn within the open- 

 ing by the contraction of several fine muscles. The apparatus in 

 the American C. mnltiscripta is as in the European C. vinula. In 

 a living specimen the large secretory sac was seen to be of the same 

 size and shape as in Macrurocampa, and of the color of raw silk. 

 The sac when distended extends back to a little behind the middle 

 pair of legs, and is nearly two-thirds as wide as the body. The 

 caterpillar sent out the fluid when handled, but we could not make 

 it spray. 



In the larva of Macrurocampa martliesia the cervical or secretory 

 gland (Fig. 366, .5) is situated in the 1st and 2d thoracic segments, 

 extending to the hinder edge of the latter and lying between the 

 nervous cord and the oesophagus and proventriculus, and when 

 empty the bulk of it lies a little to one side of the median line 

 of the body. It is partly held in place by small tracheae, one quite 

 large branch being sent to it from near the prothoracic spiracle. 

 The short, large duct, leading from it to the transverse opening in 

 the membrane between the head and prothoracic segment, is a little 

 narrower than this opening, and is kept distended by tasnidia, or a 

 series of short, spiral threads which are pale, not honey-yellowish, 

 in color. This duct lies on one side of the prothoracic ganglion, 

 resting just under the commissures passing up to the brain; it is 

 also situated between the two silk ducts. 



The very distensible sac (Fig. 366, s) is rendered elastic by a 

 curious arrangement of the cuticle, the ta3nidia of the duct itself 

 being represented by very thickly-scattered, irregular, separate, sinu- 

 ous, chitinous ridges, which stand up from the cuticular lining of 

 the wall of the sac (Fig. 366, fi). The secretory cells of the walls 

 of this sac in Cerura vinula are said by Klemensiewicz to be large 

 hexagonal cells, resembling those of silk-glands, having like them 

 large branched nuclei. 



The fluid thrown out is said by Poulton to be formic acid; it 

 causes violent effervescence when allowed to fall upon sodium- 



