228 REPORT OF THE COMMISSIONER OF AGRICULTURE, 



tion have appeared, the last pair or anal prop-legs alone varying from 

 the usual form in being united across the middle line. The spiracles 

 have become mounted on quite prominent tubercles, but their position 

 is the same as in the fiat form. The round larvae vary much in their 

 markings. Some individuals have the brown, horny dorsal j)lates which 

 ■were found upon the flat larvae ; others have not a trace of them, while 

 others still form various intermediate stages. The last four pairs ot 

 legs have the appearance of common prop-legs, but the first three pairs 

 do not at all resemble the ordinary thoracic legs of caterpillars. In- 

 stead of being horny, articulated, and apparently ending in a point, 

 they are mere fleshy tubercles, each with a depression in its center, and 

 looking much like pro-legs. 



The reasons for these remarkable changes are soon evident, for these 

 round larvae are to spin the cocoon. With the mouth parts the now 

 almost useless mandibles have become much smaller, and from being 

 the most important have become the least important of the mouth parts. 

 The parts aijpearing most prominently in the round form are the labium, 

 bearing the spinnerets, the labial palpi, the maxillae and maxillary palpi, 

 all of which help in the formation of the cocoon. The development of 

 the feet is also necessary, as they enable the larva to turn itself readily 

 in the narrow compass of the cocoon during the spinning. 



The cocoon itself is simply a delicate, semi-transparent, circular sheet 

 of white silk, stretched over a part of the bottom of the mine. It is 

 usually from 5 to 7""" (.2 to .28 inch) across, and is composed of delicate 

 fibers running in every conceivable direction. The leaf at the bottom 

 of the cocoon has a number of silken threads spun across it. The object 

 of these threads is probably, as Mr. Chambers suggests,* to make the 

 space intended for the cocoon more roomy by causing a bulge on the 

 under side of the leaf from the contracting of these fibers. 



Up to this point the life of the larva occupies from eighteen to twenty- 

 five days, and it attains an average length of about 5.4""" (A inch). 



The length of time elapsing between the completion of the cocoon and 

 the change to pupa I have not definitely ascertained ; but that it is 

 very short is shown by the fact that two larvae left engaged in spinning 

 at 4 o'clock in the afternoon had completed the transformation at nine 

 the next morning.* 



The last larval skin is extremely delicate and elastic. ' Upon being 

 shed within the cocoon it shrinks away so as to be almost imperceptible. 

 Upon comparing it with the last skin shed ivithout the cocoon it is seen 

 to be only about one-tenth its size, or rather to occupy only about one- 

 tenth its space. The utility of this is obvious when we think of the con- 

 tracted space of the cocoon. The extreme dehcacy of this last skin 

 enables one to see plainly the formation of the chrysalis within with a 

 moderate microscopic power and a strong transmitted light. 



The chrysalis is light brown in color and about 4,2"" (.10 inch) in 

 length. The most remarkable point about it is the toothed crest upon 

 its forehead, which enables it doubtless to pierce or saw through the 

 cocoon. Fig. n shows a side view, and o a front view of this crust, 

 showing the sharp teeth. The posterior end of the body is squarely cut 

 oft", and is furnished with three minute forward-curved, finger-like hooks, 

 which undoubtedly serve to hold the chrysaUs in position by hooking 

 into the silk of the cocoon during the exit of the moth, but not to any 

 extent before, as the chi-ysalis readily falls out when the cocoon is cut 

 open. As the chrysalis advances in develo])ment the colors of the con- 



•Psyclie, Tol. ii, page 150, "On Larva© of Tinebia, especially of LittiocoUetis," by 

 V. T. Cliambera. 



