1890 .] 
97 
[Packard. 
and some other Coleopterous families whose larvae bore in hard sub- 
stances. And in such groups this hard, chitinous plate serves to 
protect the base of the head and adjacent parts of the body most 
exposed to injury. Developed in the borers of widely different 
orders, and obviously of direct use to the animal, it has probably 
arisen in response to an external stimulus, an extra quantity of 
chitin having been developed by the hypodermal cells of the tergal 
arch of the prothoracic segment, which by friction has become 
thickened, just as the skin of the sole of the foot in savages be- 
comes thick and horny in those accustomed to go barefoot in dry, 
rough places. 
In the lower Lepidopterous families, as the Tineidse, Tortricidae, 
Pyralidse, as well as in the low-feeding Noctuidse, which hide un- 
der stones, such as the cut-worms, a well developed cervical shield 
is generally present. 
In the Botnbyces which feed exposed both on trees and on her- 
baceous plants the cervical shield is rarely even well developed, 
but there are sporadic cases of its development, and especially of its 
appearance in the early stages and of its suppression in later lar- 
val life, which are of interest and merit notice. 
In the Notodontian genus Cerura, the prothoracic segment is unu- 
sually broad and flat above, although it is not smooth, chitinous 
or polished : whether its use is to support the large lateral tuber- 
cles, or to resist pressure and friction is a question. 
In the first stage of Dasylophia anguina there is a small cervical 
shield (fig. 11c) which bears four glandular setae on each side of 
the median red dorsal line. 
In Datana mtegerrima, a small, transversely oblong, conspicuous, 
black, cervical shield is present in the freshly hatched larva, and in 
the subsequent stages. There is, however, no shield or rudiments 
of one in Edema albifrons , or in Heterocampa and Lochmaeus. 
In the other Bombyces there is no genuine shield, but in the first 
stage of some forms the two dorsal piliferous warts on the pro- 
thoracic segment are more or less enlarged and sometimes coa- 
lesced so as to indicate that the shield may have been formed by the 
enlargement and coalescence of these warts. 
Thus in the first stage of Hyperchiria io there is a small trans- 
verse^ narrow oval dark plate evidently resulting from the coa- 
lescence of the two dorsal piliferous warts, and bearing two large 
7 FEBRUARY, 1891 . 
PROCEEDINGS B. S. N. H. 
VOL. XXV 
