454 



CIRRHOPOPA. 



Fig. 234. 



sense, of some kind or other, there can be little doubt ; and, judging 

 from its position, Mr. Darwin is induced to consider that the two con- 

 stitute an olfactory apparatus. 



(1173.) At a little distance beneath the basal articulation of the first 

 cirrus, on each side, there may be seen a slight swelling, and on the 

 under side of this a transverse slit -like 

 orifice (fig. 234, e), one-twentieth of an 

 inch in length, in Conchoderma, but 

 often only half that size : this is re- 

 garded by Mr. Darwin as the organ of 

 hearing. The external orifice leads into 

 a deep and rather wide meatus, which, 

 enlarging upwards, is lined by a thick 

 pulpy eorium, and is closed at the upper 

 end; from its summit is suspended a 

 flattened sac, variously shaped in dif- 

 ferent genera. In all cases the sac is 

 empty, or contains only a little pulpy 

 matter ; it consists of brownish, thick, 

 and remarkably elastic tissue, formed 

 apparently of transverse little pillars, 

 becoming fibrous on the outside, and 

 with their inner ends appearing like 

 hyaline points. The mouth of the acoustic 

 sac is closed by a tender diaphragm, 

 through which Mr. Darwin thinks he 

 saw a moderate-sized nerve enter ; and 

 as the first pair of cirri seem, to a cer- 

 tain extent, to perform the office of 

 antennae, therefore the position of an 

 acoustic organ at their bases is ana- 

 logous to what exists in Crustacea ; but 

 there are not here any otoliths, or the 

 siliceous particles and hairs, as described 

 by Dr. Farre in that class ( 1050). Nevertheless the sac is so highly 

 elastic, and its suspension in a meatus freely open to the water seems so 

 well adapted for an acoustic organ, that Mr. Darwin considers such to 

 be its function. 



(1174.) With respect to the organization of the reproductive system 

 in these creatures, the most discordant opinions are expressed by dif- 

 ferent writers, no two authors agreeing either concerning the names 

 or offices which ought to be assigned to different parts of the generative 

 apparatus. It must therefore be our endeavour, in considering this 

 part of their economy, to separate as far as practicable all conjecture 

 and hypothetical reasoning from the simple facts which anatomy has 



Structure of Ccmchoderma: a, ex- 

 ternal layer of integument ; a a, in- 

 ternal layer ; b b, ova, forming a layer 

 around the body; c, ovipositor; d, 

 mouth ; e, presumed organ of hearing ; 

 f, aperture communicating with the 

 interior of the pedicle ; g, h, pedicle. 

 (After Darwin.) 



