194 PAPERS BY DR. B. CLEMENS. 



covered with a layer of damp earth an inch or two thick, and 

 packed rather firmly, that the moisture does not collect on 

 the sides of the vessel to such a degree as to endanger the 

 lives of the larvas. Indeed its accumulation may be prevented 

 entirely, provided the sand is not too wet. The earth should 

 not be wetted and its degree of dampness should be that 

 which is natural to the soil in summer. If the cover of the 

 breeding-vessel fits accurately, the leaves may be laid simply 

 on the surface of the earth, and they will keep fresh for quite 

 a long time. ' 



The cocoonets are not as easily detected by the eye, how- 

 ever, on the brown earth, as they are on the surface of white 

 sand. But if the surface of the earth is smoothed with the 

 fingers, so as to leave no fissures or cracks in it, the larva? 

 will nearly always weave on the sides of the glass where they 

 meet the surface of the earth. 



The sycamore miners often weave their cocoonets within 

 their mines, when the air within the vessel is too humid. 

 Previously to weaving they carefully cut the epidermis, some 

 distance on each side of the point at which the cocoonet is 

 to be placed, and thus secure their exit as imagos. Accord- 

 ing to my observation, this never takes place in nature. 

 And yet, great numbers of the larvae that mine leaves over- 

 hanging a stream of water — for the sycamore usually stands 

 along the margins of streams — must be drowned after abandon- 

 ing their mines. 



