Dermal Sense- Organs of the Crustacea. 301 



sliortly to publish a more detailed account, accompanied by 

 figures. 



Owing to the usually extremely hard chitlnous body- 

 covering of the Crustacea, a sensory perception, with the 

 exception of sight, can only be conveyed by means of struc- 

 tures composed of hairs. In many cases such sensory hairs 

 are externally in no way distinguishable from ordinary hairs 

 and are characterized as sense-organs only by the sense-cells 

 lying beneath their base ; in many instances, however, they 

 liave peculiar shapes, and have been described as feathered 

 seta3*, half-featheied seta3, cones, knobs, clubs, plugs, threads, 

 styles, cylinders, tubes (" Fiederborsten, Halbfiederborsten, 

 Kegel, Kolben, Keulen, Zapfen, Fiidcn, Griffel, Cylinder, 

 SchlUuche "), &c. Yet, however different and varied the 

 form of the sensory hairs of the Crustacea, they are never- 

 theless connected together by a continuous series of transitions. 

 The first antennaj of the Copepods are of especial interest, 

 since we often find upon them placed close together the 

 greatest variety of sensory hairs with the various intermediate 

 forms. 



At the spot where any kind of capillary structure, it matters 

 not whether a sensory or an ordinary hair, projects from the 

 cuticle, the latter is pierced by a more or less fine pore-canal. 

 The mode of attachment of the hair is of the greatest func- 

 tional importance ; in the majority of cases the capillary 

 structures rest upon a more or less arched, cupola-shaped, 

 chitinous membrane, which rises from the margin of the 

 pore-canal ; this membrane is sometimes soft and thin, so 

 that it gives great mobility to the hair, as is above all charac- 

 teristic of the auditory hairs. The shaft of the hair is gene- 

 rally in two parts, and consists of a stouter chitinized. proximal 

 and a paler tliin-walled distal portion, the two being distinctly 

 separated from one another by a slight constriction. 



I. Ox THE Occurrence of Dermal Sense-Organs on 

 THE Bodies of Crustacea. 



In the whole of the Crustacea belonging to the different 

 classes, orders, and families I have discovered sensory hairs 

 on almost all parts of the body. Both the first as well as the 



* Feathered setae are, as is well known, widely distributed among the 

 Crustacea and also occur in the aquatic Dipterous larvae ; I would, how- 

 ever, incidentally remark tliat feathered setae are also found in genuine 

 land-animals, e. [/. on the anterior portion (so-called tongue) of the hypo- 

 pharynx of Scutiyera, on the palp-shaped appendages of the maxillae of 

 Litkobiiis, ami on tlie pcdipalpi of male spiders. 



