324 



lav iibres, related to the excretory apparatus. The vermicular action 

 of the alimentary canal is constant and rhythmical. 



The dorsal vessel is next in size. It can be traced to the region 

 just behind the head, where it shows a disposition to curve downwards ; 

 though neither here, nor at the opposite extremity, could I detect the 

 continuity between this vessel and the recurrent vessels or streams. 



The ventral or recurrent streams are at least two in the middle 

 region of the larva. There are all the usual indications of vascular walls ; 

 but the general doubt entertained amongst anatomists, as to the exist- 

 ence of such walls In any insects, causes me to withhold the allegation of 

 their occurrence here. Posterior to the middle region, these streams 

 pursue a somewhat convoluted course, but do not assume any thing like 

 the sinus-disposition seen in certain worms : the circulating fluid could 

 be distinctly traced, flowing backwards with an irregular movement 

 through nearly the whole length of the larva. 



The tracheary system is beautifully distinct. Stigmata occur along 

 the sides at points corresponding to the feet and pedal swellings, and 

 connect by large trunks with a somewhat sinuous longitudinal vessel, 

 which runs from the head quite around the animal, being somewhat 

 reduced in size in the neighborhood of the hinder extremity. These 

 longitudinal trunks are connected, in each segment, by a single trans- 

 verse trunk ; but, in the segments which bear the three pairs of feet, 

 the transverse trunks are in pairs. From the trunks arising from the 

 stigmata, but especially from the longitudinal trunks, arise branches 

 which ramify throughout the body. The transverse trunks are also 

 somewhat branched. 



No trace of a nervous system was detected. 



Immediately after the slug escapes from the egg, it begins to feed 

 upon the green pulp of the leaf, and thus by degrees covers the leaf 

 with small, round, faded spots. The brood began to attain the full 

 growth aiid to disappear about the middle of July. It would seem 

 that their retirement to the chrysalis state may be somewhat hastened 

 by external circumstances. The stem of a small dwarf pear-tree, 

 which had been completely denuded by these depredators, was seen 

 to be covered with slugs of various ages, all alike winding their way 

 towaixl the ground. Dozens of the lai'vaj were seen already squirm- 

 ing upon the surface of the soil. The next day, all had disappeared. 



The autumn brood of our cherry-slug may be regarded as a com- 

 plete failure ; the fly barely making its appearance early in September, 

 and the slugs being scarely discoverable. 



This saw-fly, in reference to which I have offered some facts which 

 I have not found on record, differs as much from the slug-fly of Boston 

 as that does from the Selandria wthiops of Europe : whether the three 

 forms are to be regarded as sj^eeifically identical, will depend some- 



