Larva of Goat Moth. 81 



graph of the anatomy of this larva, and bent round so as to lie 

 in apposition with the bladder into which it opens, and in the 

 interval between it and the stomach. The bladder, with the pos- 

 terior extremity of which this tubular gland is thus connected, 

 opens anteriorly by means of a wide duct into the mouth ; and the 

 organ thus made up of a duct, a bladder-like receptacle, and a 

 tubular gland, may be seen to correspond with the much smaller 

 salivary glands of the perfect insect. Neither upon the fasciculi of 

 tracheae which are seen passing inwards from the spiracles to dis- 

 tribute themselves to the viscera, nor upon the longitudinal canals 

 connecting the stem whence these fasciculi spring, which may be 

 seen here and there in the intervals left between the lobes of the 

 ' fat body,^ are there any vesicular dilatations developed in the 

 larval state. This relatively inferior evolution of the respiratory 

 system may be explained upon purely mechanical grounds, when 

 we consider the comparatively sluggish movements of the larva, 

 whilst the physiological necessity which exists during periods of 

 growth and development for an active performance of the renal 

 functions, will account for the large development of the Malpighian 

 vessels here observable. And the all but complete absorption and 

 disappearance of the ' fat body^ at the end of the metamorphoses 

 of metabolous insects, is to be explained by the need they have, 

 especially during their period of existence, as pupae, for a large 

 supply of force and matter, for the carrying out of the complex 

 changes in, and the superadditions to, the larval organism which the 

 arrangements of the muscles and the evolution of the reproductive 

 organs in the imago may be taken as illustrating. Such dif- 

 ferences in the digestive apparatus of the larva as those already 

 spoken of (Prep. 25, p. 75) in the appendages of the oral segments, 

 as the larger calibre and the lesser length of the digestive canal, as 

 the absence of convolutions, and of a crop, and as the much larger 

 size of the salivary glands, are obviously correlated with the dif- 

 ferences existing between its mode of sustenance and that of the 

 butterfly. The presence of a rectal coecum in the perfect insect, 

 is to be noted as an additional point of contrast. The disappear- 

 ance of the silk-glands during the pupa-stage is readily explicable 

 by the fact, that all need for such organs ceases after the forma- 

 tion of the cocoon ; and the condition of semi-fluidity to which the 

 various organs of the pupa are reduced in the early stages of the 



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