SOME SINfiULAK llllNdS ABOUT CATERPILLARS. H31 



tril)ut(.'il with great ri'gularitv. iu wliich a transversic is more often seen 

 than a longitudinal direction, t^onietinies dispersed indiscriminately all over 

 the body. ^\'lK■n a transverse arrangement olitaiiis, it is usually related 

 closely to tiie sections into wliicii the segments arc di\ided. The use of 

 this clothing for the body is tolerably clear, since this pile must prevent 

 the too rapid evaporation of tlie heat fron) tiie surface of the body ; for, al- 

 though caterpillars would be classed among the cold-blooded animals, 

 they nevertiielcss have an internal heat above that of the surrounding at- 

 mosphere, wliich originates from tlie activities of the organs and the re- 

 spiratory function, and wliich they would lose more rajiidly but for this 

 investing pile. 



But there are two other series of structures, always arranged in longitu- 

 dinal rows, the use of which is wholly unknown. One of these is a universal 

 characteristic of all caterpillars in their earliest stage, excepting probably 

 the larger part of the highest family, and is common to the later stages of 

 some ot' the lower families ; and that is the special papilla-mounted bristles 

 which are fui'nished witli an expanded trumpet-mouthed tip and are the 

 ducts leading from glands at their base which secrete a transparent fluid, 

 wliich, after secretion, is borne in a little globide in the mouth of the 

 trumpet, and sometimes kept in its place by a few microscopic bristles 

 which surround its rim. That these have some protective function is 

 highly probable, l)ut what its nature may be or how it acts, is quite un- 

 known. That they may be odoriferous seems highly improbable, for, 

 though we can easily conceive that their insect enemies might perceive an 

 odor from them, did such exist, which would be imperceptible to our senses 

 (as we have the best reason for believing is the case with minute odorifer- 

 ous organs of the perfect insect), yet we have not a particle of evidence to 

 this effect, since in not a single instance have we been able to perceive any 

 odor whatever from them. In the case of the organs of the mature forms, 

 we conclude them to be odoriferous because in a few instances we can per- 

 ceive an odor, and may fairly argue that entirely similar structures in 

 others from which we can perceive no odor give off, nevertheless, some scent. 

 Such evidence is absolutely wanting with regard to the present structures, 

 and their use is therefore a subject for research. On experimenting, how- 

 ever, with some of the caterpillars of Pierinae which bear them when full 

 grown, I have found the globule at the summit to be visibly increased 

 when the creature was disturbed. 



There is still another structure only recently made known, the purpose 

 of which is obscure. These are the crateriform, chitinous annuli, which 

 are ranged in longitudinal rows along the abdominal and sometimes the 

 thoracic segments. They are found only in certain groups, but appear to 

 be a universal characteristic of the earliest stage of the Lycaenidae, and 

 have the appearance of spiracles, only they are ordinarily quite circular, 



