76 Dr. MSrch on the Homology of 



like organs, which are always provided with corneous hooks, 

 are evertile; but this has been established by Eydoux and 

 Souleyet* in the genera Pneumodermon and Clione. 



The long arms of the decapod Cephalopods seem to me with- 

 out doubt the same organs as the cheek-hooks of Gymnosomata; 

 thcv have the same latero-ventral position, and are retractile 

 within a cavity or pouch inside the short arms, which may be 

 considered as a single fissured veil, and perform the same func- 

 tion in the animal. Prof. Loven considered the long arms of 

 Decapoda homologous with the tentacula (vibracula) of the Gas- 

 teropoda, and compared them specially with the rhinophores of 

 Doris. I do not believe that this homology is natural, because 

 the tentacula are always dorsal, and the " long arms " of Cephalo- 

 poda always latero-ventral. It seems also very doubtful whether 

 an organ of prehension can be homologous with an organ of 

 smell. If the Cephalopoda have no tentacula at all, the " cretes 

 auriculaires " (D'Orb.) or " paupieres inferieures" (D'Orb.) of 

 the Myopsid Decapods may be considered as their homologue. 

 The triangular filaments over the eyes of Octopi are perhaps, too, 

 a form of tentacula. I believe they are provided with a nervous 

 ganglion at their base, like those of Doris. 



The " organe en pioche," in Conus, of Quoy and Gaimard is 

 a tubular sac, provided with arrow-like corneous hooks with a 

 hollow channel, which are considered venomous. I have had an 

 opportunity of confirming the exactness of the anatomy repre- 

 sented in the ' Voyage de 1' Astrolabe/ As these hooks are not 

 situated in the true oral tube, it is still very doubtful whether 

 they really can be considered to belong to the radula. I 

 suppose these arrow-like hooks are more allied to the cheek- 

 hooks of Gymnosomata. As the hooks turn their points in 

 opposite directions in the two arms of the pouch, it is probable 

 they are evertile each in a different direction, but how and through 

 what aperture is not yet discovered. 



On the Palpi and Lips. 



There are often in the Gasteropoda two different apertures in 

 the same animal, called mouths. The true mouth is the anterior 

 opening of the bulbus pharyngeus, frequently prolonged into an 

 haustellum. This opening is only provided with the hard plates 

 described above. The outer or false mouth is a simple slit in 

 the skin, containing the lips or palpi, but never any mandibles; 

 and it forms a passage for the protrusile haustellum, which, in 

 a retracted state, is concealed in a cavity behind this slit. 



In the Acephala the palpi are represented by two pairs of 



* Voyage de la Bonite; Mrs. Gray's figures of Moll. t. 255. f. 3. 



