﻿LARVA 



325 



little spaces placed on 

 they are called "ocelli," 

 each of these external 



Fig 



d 



h- .-» \^ e 



9 



166. — Front view of head of 

 a caterpillar, with the jaws 

 partially opened. ", Lai mini ; 

 b, mandible ; c, antenna ; d, 

 ocelli ; e, maxilla ; /, lingua ; g, 

 spinneret ; />, labial palp. 



fewer, transparent, somewhat prominent 

 each side of the lower part of the head; 

 by Landois " ocelli compositi." Under 

 facets there are placed percipient 

 structures, apparently very imperfect 

 functionally, the caterpillar's sight 

 being of the poorest character. 1 The 

 spiracles of the caterpillar are nine 

 on each side, placed one on the first 

 thoracic segment and one on each of 

 the first eight abdominal segments ; 

 there are no true stigmata on the 

 second and third thoracic segments, 

 though traces of their rudiments or 

 vestiges are sometimes visible. 



In the caterpillar there are no traces of the external sexual 

 organs, so that the two sexes cannot be distinguished on super- 

 ficial inspection ; it was however long ago demonstrated by 

 Herold 2 that the ovaries and testes exist in the youngest cater- 

 pillars, and undergo a certain amount of growth and development 

 in the larval instars ; the most important feature of which is 

 that the testes are originally separate but subsequently coalesce 

 in the middle line of the body, and become enclosed in a common 

 capsule. In a few forms — especially of Liparidae — (Lymantriidae 

 of modern authors) — the caterpillars are said to be of different 

 colours in the two sexes. Most of what is known on this point 

 has been referred to by Hatchett Jackson. 3 



The Silk-glands of Lepidoptera are of great interest from the 

 physiological point of view, as well as from the fact that they 

 have furnished for many ages one of the most beautiful of the 

 adornments made use of by our own species. The sericteria, or 

 vessels that secrete silk, are of simple structure, and differ greatly 

 in their size in the various forms of the Order ; they sometimes 

 become of great length ; in the Silk-worm each of the two 

 vessels is nearly five times as long as the body, while in 

 Bombyx yamamai and others, even this is exceeded. They 



1 See Plateau, Bull. Ac. Belgique, xv. 1888, p. 28 ; in reference to structure of 

 ocelli, Blanc, Tete dn Bombyx mori . . . 1891, pp. 163, etc. ; and Landois in 

 Zeitsehr. uHss. Zool. xvi. 1866, p. 27. 



- Entwickelungsgesehichte der Schmetterlinge, Cassel, 1815. 



3 Tr. Linn. Soe. London, Zool. 2nd Ser., v. 1890. pp. 147, 148. 



