Among insects and Crustacea there are a great number of peculiarly formed skin appendages, for which it is very difficult to suggest any probable function.
The lower antennæ of the male in Gammarus, for instance, bear a very peculiar slipper-shaped organ, situated on a short
| Fig. 3.—Edge of a portion of the Mantle of Aglaura hemistoma, with a pair of Sense-Organs (after Hertwig). v, velum; k, sense-organ; ro, layer of nettle-cells; t, tentacle. | Fig. 4.—Sense-Organ of Leech (from Carrière, after Ranke). 1, epithelium; 2, pigment; 3, cells; 4, nerve. The longer axis equals 4 mm. |
stalk: this was first mentioned by Milne-Edwards, and subsequently by other authors, especially by Leydig.[1] The short stalk contains a canal, which appears to divide into radiating branches on reaching the "slipper," which itself is marked by a series of rings.
Among other problematical organs, I might refer to the remarkable pyriform sensory organs on the antennæ of Pleuromma,[2] the appendages on the second thoracic leg of Serolis, those on the maxillipeds of Eurycopa, on the metatarsus of spiders, the finger-shaped organ on the antennæ of Polydesmus, the singular pleural eye (?) of Pleuromma, and many others.
There is every reason to hope that future studies will throw much light on these interesting structures. We may, no doubt, expect much from the improvement in our microscopes, the use of new reagents, and of mechanical appliances, such as the micro-tome; but the ultimate atoms of which matter is composed are so infinitesimally minute, that it is difficult to foresee any manner in which we may hope for a final solution of these problems.
Loschmidt, who has since been confirmed by Stoney and Sir W. Thomson, calculates that each of the ultimate atoms of matter
