PROBLEMATICAL ORGANS OF SENSE. 105 



Among insects and Crustacea there are a great number of pe- 

 culiarly formed skin appendages, for wliich it is very difficult to 

 suggest any probable function. 



The lower antennse of the male in Gammarus, for instance, 

 bear a very peculiar slipper-shaped organ, situated on a short 



Fig. 3.— Edge op a portion op the Mantle op Aglaura Fig. 4.— Sense-Organ op Leech (from 



hemistoma, with a pair op Sense-Organs (after Herf- Carriere, after Eanke). 1, epithelium; 



wig). V, velum ; k, secse-organ ; ro, layer of nettle- 2, pigment ; .3, cells ; 4, nerve. The 



cells ; t, tentacle. longer axis equals -4 mm. 



stalk: this was first mentioned by Milne - Edwards, and subse- 

 quently by other authors, especially by Leydig.* 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 miglit refer to the remark- 

 able pyriform sensory organs on the antennae of Pleuromma,f the 

 appendages on the second thoracic leg of Scrolls, those on the 

 maxillipeds of Eurycopa, on the metatarsus of spiders, the finger- 

 shaped organ on the antennse 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 comi)osed 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 



* " Zeit. fiir wiss. Zool.," 1878. 



•J- Brady, " On the Copepoda of the Challenger Expedition," vol. viii. 



