REPORT ON THE CIRRIPEDIA. 23 



II. SEGMENTAL ORGANS IN THE CIRRIPEDIA. 



Cirripedia are rich in organs of an unknown or at least problematic function. One 

 instance of these is found in the " olfactory organs " or sacs of Darwin. " In the 

 outer maxillae," Darwin says, 1 :t at their bases where united together, but above the basal 

 fold separating the mouth from the body, there are, in all the genera, a pair of orifices ; 

 these are sometimes seated on a slight prominence, as in Lithotrya, or on the summit of 

 flattened tubes projecting upwards and towards each other as in Ibla, Scalpellum, and 

 Pollicipes. In Ibla these tubular projections rise from almost between the outer and 

 inner maxillae. It is impossible to behold these organs, and doubt that they are of high 

 functional importance to the animal. The orifice leads into a deep sack lined by pulpy 

 corium, and closed at the bottom. The outer integument is inflected inwards (hence 

 periodically moulted) and becoming of excessive tenuity, runs to near the bottom of the 

 sack, where it ends in an open tube; so excessively thin is this inflected membrane, that 

 until examining Anelasma, I was not quite certain that I was right in believing that the 

 outer integument did not extend over the whole bottom. I several times saw a nerve of 

 considerable size entering and blending into a pulpy layer at the bottom of the sack of 

 corium ; but I failed in tracing to which of the three pair of nerves, springing from the 

 front end of the infra-cesophageal ganglion, it joined. I can hardly avoid concluding that 

 this closed sack, with its naked bottom, is an organ of sense ; and, considering that the 

 outer maxillae serve to carry the prey entangled by the cirri towards the maxillae and 

 mandibles, the position seems so admirably adapted for an olfactory organ, whereby the 

 animal could at once perceive the nature of any floating object thus caught, that I have 

 ventured provisionally to designate the two orifices and sacks as olfactory." 



This supposition of Darwin's has, however, been accepted with great reserve. As far 

 as my knowledge of the literature of the group goes, the same organs have not been 

 studied, nor has another opinion been published about their function since Darwin's. 2 

 I first tried to get a good insight into the structure of this apparatus by isolating the 

 outer maxillae. I arrived at the same conclusion as Darwin, viz., that it was composed 

 of a duct with an outward orifice and an internal portion, a kind of sack lined by a layer 

 of cells different in structure from those of the duct. In some of the figures representing 

 parts of the mouth of species of the genus Scalpellum (e.g. Scalpellum parallelogramma, 

 Scalpellum stromii, &c), in the systematic part of my report, the long and very 

 characteristic tubes at the extremity of which the orifices are found have been represented. 

 I then studied the apparatus by the aid of transverse sections of the thorax of the 



1 Darwin, Lepadid;v, 1851, p. 52. 



- Claus (Lehrb. d. Zool. 3 Aufl. 1876, p. 456, says :— "Gehor- imd Geruchsorgane sind nicht mit Sicherheit nachge- 

 wiesen, da die von Darwin als solche in Anspruch genommenen Bildungen eine andere Deutung (Oviducte, Driisen- 

 bffnungen) erfahren haben." I do not know where this opinion has been published, so far as Darwin's olfactory organ is 

 concerned. 



