mVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 783 



produced by the followiug insects : P. sjnrothecce (gall formed of 

 the twisted petiole), Pacliypaiypa marsupialis (gall in the form of a 

 purse, generally red and compressed laterally, projecting from the 

 upper side of the leaf). Pemphigus bursariiis (gall growing either on a 

 branch or a petiole), P. populi n. sp. (gall insufficiently studied, but it 

 is believed that the tissues of the median nervure take the greatest 

 part in its constitution), P. affinis (hardly to be considered a " gall," 

 consisting simply of a folding of the leaf on the median nervure, the 

 right and left margins meeting and forming a large cavity between 

 the two parts of the leaf), P. vesicarius (gall possibly resulting from 

 the union and abnormal growth of the leaves of a bud). 

 The following are M. Courchet's conclusions : — 

 1st. None of the galls produced by the aphides arise from the 

 very centre of the tissues of an organ ; some commence by a simple 

 invagination of the lamina of a leaf (" horn gall," utriculate gall of 

 the Terebinth), or by a cellular swelling which forms and rises little 

 by little around the insect as in the gall of Pemyliigns bursarius of 

 the Black Poplar ; or again, a petiole coiled up on itself encloses the 

 insect in a cellular utricle which finally becomes a true gall, as 

 happens in the case of P. spirothecce, &c. ; in other words, all may be 

 classed under M. de Lacaze-Duthiers' term of " false internal galls." 

 2nd. Their cavity is always spacious, and the wall relatively thin, 

 which is rendered necessary by the presence in their interior of an 

 always considerable number of living insects. 



3rd. Their structure always retains more or less of that of the 

 organ which bears them, and which is entirely, or in part, transformed 

 to j)roduce them. In general their walls are composed of a tolerably 

 homogeneous fundamental cellular tissue, which is traversed by fibro- 

 vascular bundles in variable number. There are no well-marked 

 concentric layers here, as seen, for instance, in the galls produced by 

 Cynips on the oak. 



4th. All the galls of aphides hitherto observed by the author, 

 with one exception, represent appendicular organs, or parts of 

 appendicular organs transformed ; the gall of Pemphigus bursarius 

 alone is formed laterally on an axis or petiole by a single prolifera- 

 tion of the herbaceous layer, and in an independent manner. 



/3. Myriapoda. 



Eyes and Brain of Cermatia forceps.* — Mr. N. Mason lias made 

 preparations of the eyes of this Myriapod, which is useful as a sjjider- 

 destroyer, and Dr. Packard gives the result of his examination of tho 

 eyes and brain. 



The eye appears to be constructed on tho same plan as that of 

 other species of tho sub-class, but differing in important resjiccts. 

 Though Cermatia is said to have compound eyes in contradistinction 

 from the so-called " ocelli " of other Myriapods, the latter arc like- 

 wise truly aggregated or compound, tho " ocelli " being composed of 

 contiguous facets, tho nerve-fibres supplying them arising in tho 



♦ ' Am. Nut.,' xiv. (1880) i\ C02. 



