234 PROCEEDINGS OF THE ACADEMY OF [1883. 



organ similar to the side line, or side organ, that has been found 

 in the annelides by Eisig' and Meyer.- The ganglion olfaetorium 

 may be one of a pair which would represent anothet segment, the 

 mate of which has been lost by the disturbance of the bilateral 

 symmetry. This so-called ganglion olfaetorium is paired in the 

 lowest Gastropoda, as Patella^ Haliotis, etc., when the bilateral sym- 

 metry is not as disturbed as in tlie higher forms of Gastropoda. 



The 07'gan of touch, — Moqun-Tandon makes the following 

 observation : '■'•Ancylus does not possess an especial organ of touch. 

 The foot, which is large, flexible and capable of being exactly 

 applied to solid bodies, and embraces them in part, it is true, 

 receives and transmits tr^ct le impressions, but the animal rarely 

 uses it for this pui"pose. 



" Blainville has proved that the tentacles of the Gastropoda 

 never serve as organs of touch, in spite of their sensibility; he 

 has merely confirmed the opinion of many earlier naturalists. 



" This is not the case with the anterior part of the head, with 

 which the mollusk at times touches different bodies with the 

 appearance of smelling them. I have seen two individuals, which 

 were about to copulate, which had the air of feeling and caressing 

 themselves with the mouth.^ " 



Moquin-Tandon was wrong when he said that no especial organ 

 of touch was present in Ancylus, for I have found one without 

 any difficulty. It is probable that Moquin-Tandon was unable to 

 find it, as he did not make any sections of the animal. As would be 

 supposed from the citation, the organ lies in the anterior part of 



1 Die Seitenorgare und becherformige Organe der Capitelliden. Mit- 

 theil. a. d. Zool. Stat, zu Neapel, Bd. i, 1879. 



' Zur Anatomie und Histologie von Polyopthalmus pictus. Clap., Archiv 

 f. Microscop. Anat., Bd. xxi, 1882. 



3 "L'Ancyle iie possede pas d'organe special pour le toucJier active. Son 

 pied, qui est large, souple et susceptible de s'appliques exactement contra 

 les corps solids, meme de les embrasser en partie peut, il est vrai, recevoir 

 et transmettre de impressions tructiles mais I'animal I'emploie rarement a 

 cet usage. 



" Blainville a prouve que les tentacles des gastrop tdes ne servaient jamais 

 a I'exploration du tact, malgre leur sensibilite ; il n'a fait que contirmer 

 1 opinion de plusieurs anciens natiiralistes. 11 n'est pas de meme du 

 chaperon et du moufle, avec lesqnel le MoUusque touche quelqnefois les 

 divers corps et semble les ttaiver j'ai on doux individus di.spose a 

 s'acconpler. qui avaient I'air de se pali>er et de se carresser avec la bouche." 

 — Reclier. anat. pliysiol, s. I'Ancyle, etc , p. 131. 



