NOTODONTID^. 97 



rough externally but highly polished inside, composed of a 

 kind of gum secreted by the larva mixed with small frag- 

 ments bitten from the surface where it is placed ; on the 

 trunk of a tree, usually rather near the ground in an angle 

 of the bark, which it closely resembles. (C. Fenn.) The 

 resemblance of the cocoon to the bark is so close that it is 

 almost impossible to discover it with the eye. Not always 

 placed upon the tree on which the larva has fed, but the 

 cocoon (which is easily found when vacated by the moth) has 

 been known to be placed on trunks of oak, birch, horse- 

 chestnut and other trees, and even on the mortar of a wall, 

 or on a potato tuhcr. Colonel Partridge found a number of 

 cocoons, one of which contained a living pupa, on stems of 

 Tamarisk (Tamarix gallica) at the Isle of Portland, but 

 as neither poplar, sallow, nor any known food plant of the 

 species grew near by, the inference appeared probable that 

 the larvas had fed on that unusual plant. Dr. T. A. Chapman 

 has shown that the portion of the cocoon through which the 

 moth has to break is thinner, more transparent and less 

 strengthened with bits of bark than the remainder of the 

 cocoon, that the pupa has a sort of edge, or keel, in front, 

 for cutting its way, and that the moth, as it breaks the pupa 

 skin, emits a fluid from an orifice close to the small filaments 

 of the tongue, which fluid has the power of softening the 

 cocoon, and is rubbed round inside by the moth before forcing 

 its way out. This is of great interest, since the cocoon is of 

 extraordinary hardness, and utterly impervious to so soft an 

 insect without such aid. Professor Poulton states that the 

 fluid in question is powerfully acid, affecting litmus paper in 

 a most marked degree, and causing violent effervescence 

 when allowed to fall upon sodium bicarbonate. He also 

 states that it is formic acid, and that the freshly opened 

 and moist cocoon is also acid to test paper. For his 

 observations on eversible glands in this and other species, 

 and the use of them for defence, for which I am unable 

 to find room here, the student is referred to the Transac- 

 VOL. III. G 



