Dermal Sense- Organs of the Crustacea. 303 



by Claus * for Nehalia and Phronima that it Is not until tlie 

 animal arrives at sexual maturity that they attain their full 

 number. In a similar way it has long been known that in 

 blind Crustacea the number and size of the olfactory tubes ia 

 more considerable than in their allies with full visual power, 

 e. g. in Asellus cavaticus and Gammarus puteanus. The mode 

 of attachment of the olfactory tubes to the cuticle is of such 

 a kind as to exclude any great degree of mobility for the 

 hair, and we can therefore hardly suppose them to be auditory 

 organs. Whether the usually bluntly rounded distal end of 

 the structures we are discussing is closed by a delicate mem- 

 brane, as Claus insists, or is open, as stated by Leydig, is 

 ditficult to determine. Tlie hair appeared to me to be closed 

 in many cases and open in others ; moreover, these extremely 

 delicate structures are often damaged at the tip. I would on 

 no account advise treating these organs with liquor potassse, 

 since I have often convinced myself, in the case of Myriapods, 

 Insects, and Crustacea, that after boiling unmistakably closed 

 olfactory cones or tubes in a weak solution of potash a distinct 

 opening became visible, since the delicate closing membrane 

 had simply disappeared. I liave, however, been able to 

 determine by' a series of experiments that in Crustacea the 

 closing membranes of the olfactory tubes are so thin as to 

 present no obstacle to delicate sensation, while fluids are able 

 to penetrate them very easily, and to come into direct contact 

 with the nerve-end apparatus. Into a saturated aqueous 

 solution of hieu de Lyon^ or methylene blue, I put a large 

 number of small living Crustacea, e. g. AseUus, Oanimarus, 

 and different species of Cladocera, and then fished out speci- 

 mens at different intervals, some after one hour, others later. 

 A stay of three to four days in these dyes does not injure an 

 Asellus in the least ; on the contrary, on being washed in 

 fresh water and examined under the microscope these Isopoda 

 appear perfectly lively. In the animals upon which I experi- 

 mented the tips of the olfactory tubes had invariably become 

 coloured first ; the dye then gradually spread as far as the 

 base of the hair, and after a longer period had elapsed the 

 nerve-end apparatus was also found to have become stained. 

 I made a similar experiment upon larger Crustacea, such as 

 Astacus, by cutting off from the living animal the first antenna 

 at its base and laying it in the solution. Staining at once 

 began to take place at the tips of the olfactory tubes, and 

 then penetrated slowly downwards. As a matter of course, 



* Claus, " Ueber den Orgauismus der Nebaliiden imd die systematischo 

 Slelluug der Leptostraca," Arbeiteii aus d. Zoolog. Institut der Uuiv. 

 Wicu, 1889; " l)er Urgaiiismus der Phrouiuuden,' ibid. 187U, 



