ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 211 



sensory organs of Insects. He finds that, with the exception of the optic 

 and auditory organs, they are all modifications of a single type, which 

 is thus described. With the stout chitinous covering of Arthropods, 

 sensory perceptions are obtained by the intermediation of more or less 

 modified hairs. Some of these are, externally, so little different from 

 ordinary hairs, that it is only by the sensory cells at their base that we 

 are able to distinguish them ; others have definite forms, and sometimes 

 a membrane-like plato of chitin is formed by the flattening out of the 

 basal portion and the reduction of the proper hair ; in this case the plate 

 closes superiorly the canal which traverses the chitinous layer. This is 

 the case with the so-called closed pits of the Hymenoptera and with 

 similar organs found by the author on the antenna? of Beetles 

 (e. g. Cetonia) ; these he proposes to speak of as membranous canals. 



Hair-like structures may be found on the surface of the cuticle, or 

 rise up from the base of a more or less deep pit in the chitin (so-called 

 sensory cones) ; one pit may contain two or more sensory cones, as in 

 the antennas of various Diptera ; the cases in which a wholo area beset 

 with a number of sensory hairs has been invaginated to form a large 

 vesicular pit, are especially interesting ; such are the large pits of the 

 antenna? of the Muscida?, and the large flesh-like pits which the author 

 has found at the tip of the labial palp of Lepidoptera. By a similar 

 process many simple chitinous pits may be united into a single large 

 pit ; such are to be seen in the antenna? of the cockchafer. 



At the base of each sensory hair there is occasionally a single 

 sensory cell, but in most cases there is a group of cells ; the former may 

 be seen in the labial palp of the Lepidoptera, where a distinct process 

 of a single large sensory cell enters each sensory hair. The sensory 

 cells are supplied by a nerve entering from behind, and the cells them- 

 selves give off long fine processes into the hair-like structures. The 

 group of sensory cells is invested in an envelope of connective tissue, 

 which consists of flat cells with flattened nuclei. When a number of 

 sensory hairs are united on one area, the groups of sensory cells which 

 belong to them may likewise be formed into a compact mass. In this 

 apparently single ganglion the arrangement of the cells can be made out, 

 and their connective-tissue investments detected ; such aggregations of 

 sensory cells may be well seen in the palps of Melolontha or Coccinella. 



In the antenna? of some insects, the palps of Coccinella, Chrysomela, 

 and Cetonia, or the gustatory organs of Hymenoptera, groups of special 

 large cells may be seen beneath the groups of sensory cells, in the 

 neighbourhood of the nerves ; notwithstanding their position, it seems to 

 be certain that these are not special sense-cells. 



The author proceeds to state what sensory organs he has observed 

 in different groups of Insects, into the details of which it is impossible 

 for us to follow him. 



Salivary glands of Insects.* — Herr A. Kniippel has examined the 

 structure of the salivary glands of insects, especially Blatta orientalis, 

 and has come to conclusions which are not in accord with those of Prof. 

 Kupffer. He finds, in fact, that the enlarged origins of the efferent duct 

 are not intracellular, but extracellular in B. orientalis; on the other 

 hand, in the cells of proboscis-glands of the Diptera, there are secretion- 

 spaces, which arc connected with the efferent ducts of the gland-cells ; 



* Arch. f. Niiturgesd)., lii. (1SSG) pp. 2G9-i}04 (2 pis.). 



