M. A. Humbert on Niphargus putcanus, var. Forclil. 249 



wliich sccni to mc to be tlie most frequent, tlic comjilication i.s 

 a little greater. Thus two or three secondary tilaments often 

 originate upon the ])rincipal one. I liave also represented a 

 iilamcnt of peculiar appearance, destitute of longitudinal fur- 

 row, and emitting from its extremity six or seven secondary 

 filaments, which are slender from their origin, and one of 

 which is particularly elongated. 



It is absolutely impossible for me to form any judgment as 

 to the functions of these capsules and their filaments ; but, 

 alfhougli I have been unable to ascertain the entrance of a nerve 

 into their interior, I think they must have some sensitive 

 function. 



The antennse have several kinds of sensitive organs. Be- 

 sides the sensitive sefce wliich are organized like those of Garn- 

 manis neglectus, so well described by 8ars, we find in them 

 olfactory cylinders, sensitive capsules, olfactory seta-, and, lastly, 

 what 1 have called hyaline bacilli. These last organs are 

 usually borne by the joints in pairs, from the fourth joint of 

 the flagellum (var. onesiensis), or the sixth (var. Forelii), to 

 the sixteenth. The last joint also bears a bacillus ; but this 

 is much shorter than the others and of a more clumsy form. 

 It is situated quite at the extremity of the joint, like the setae 

 in the midst of which it is placed. 



The bacilli are of pretty uniform diameter throughout, 

 being only a little constricted in their middle region, and 

 slightly inflated in their terminal portion. Their extremity 

 is rounded and completely closed. Their diameter at the 

 base is equal to one half or two thirds of that of tiie peduncle 

 of the olfactory cylinders ; their length is not quite half that 

 of the latter organs. They are entirely pale, without any 

 apparent structure ; no enveloping membrane can be distin- 

 guished in them. Standing in the same direction as the 

 olfactory setae and cylinders, they are nearly straight, pre- 

 senting at the utmost a slight undulation. The length of 

 these bacilli is from 0-033 to 0-038 millim. ; that of the last 

 joint is not more than from 0-008 to O'OIS millim. in length. 



These organs perfectly resemble those figured by Sars upon 

 the joints of the outer branch of the superior antenna? of 

 Mysis Qculata. This author only mentions them as " j)eculiar 

 cylindrical ajjpendages, of a very delicate nature, which occur 

 along the inner border of the first part of this branch." 



In a memoir on the sensitive organs of the antennas in dif- 

 ferent Crustacea, Claus has figured an antenna of the second 

 ])air in a Cypris, in which the inner margin of the third joint 

 bears an elongated spadiciform apj)endage which greatly 

 resembles the hyaline bacilli of Niphargus. But in the Cypria 



Ann.d) Man. X Hist. Ser. 4. Vol. xix. 17 



