20 HISTORY OF CRUSTACEA. CHAP. IV. 



the flagellum of the anterior antennae of delicate fila- 

 ments which Spence Bate calls "auditory cilia," and 

 which I have considered to be olfactory organs, as 

 did Ley dig before me, although I was not aware of 

 it. Thus they form long dense tufts in the males of 

 many Diastylidae, as Yan Beneden also states with regard 

 to Bodotria, whilst the females only possess them more 

 sparingly. In the Copepoda, Glaus called attention to 

 the diiference of the sexes in this respect. It seems to 

 me, as I may remark in passing, that this stronger deve- 

 lopment in the males is greatly in favour of the opinion 

 maintained by Leydig and myself, as in other cases male 

 animals are not unfrequently guided by the scent in 

 their pursuit of the ardent females. 



Now, in our Tanais, the young males up to the last 

 change of skin preceding sexual maturity resemble the 

 females, but then they undergo an important metamor- 

 phosis. Amongst other things they lose the moveable 

 appendages of the mouth even to those which serve for 

 the maintenance of the respiratory current ; their in- 

 testine is always found empty, and they appear only to live 

 for love. But what is most remarkable is, that they now 

 appear under two different forms. Some (fig. 3) acquire 

 powerful, long-fingered, and very mobile chelae, and, 

 instead of the single olfactory filament of the female, 

 have from 12 to 17 of these organs, which stand two or 

 three together on each joint of the flagellum. The others 

 (fig. 5) retain the short thick form of the chelae of the 

 females ; but, on the other hand, their antennae (fig. 6) 

 are equipped with a far greater number of olfactory 



