236 PROCEEDINGS OF THE ACADEMY OP [1883. 



terminal branches of that nerve which arises in the cerebral 

 ganglia, and are distributed to this region of the head. They 

 enter, as near as I could determine, the posterior end of the cell, 

 and become joined to the posterior end of the nucleus. The 

 opposite point of the nucleus approaches the free surface of the 

 cell, and probably is connected in some way with the cilia (PL X, 

 fig. 9 a). In this figure, the muscular and connective-tissue fibres 

 are intentionally omitted, as it would be diflficult to distinguish 

 the nerve-fibres, were they drawn in. 



The other organs of special sense in Ancylus are so little different 

 from those in other Pulmonata, that I do not consider it necessary 

 to give a description of them here. 



III. — The Anatomy of the Excretory Organ. 



As yet, no one has completely described the excretory organ of 

 Ancylus. This organ has only been known in part, and described 

 under various names. C. Vogt,' in the year 1841, spoke of an 

 organ imbedded in the mantle which he called the " sulphur-yellow 

 body " (Schwefelgelber Korper), and supposed that the so-called 

 reticulated portion was the lung. 



Moquin-Tandon also considered this organ an organ of respira- 

 tion, and said : " The breathing organ of Ancijlus is neither a tube 

 nor an external gill, it is an internal pouch. I am convinced of 

 this, after numerous dissections. This pouch is small, oblong, 

 straight and situated in the left side of the mollusk, toward the 

 border of the mantle, and in advance of the rectum."^ 



Blainville^ is of the same opinion, and considers that the orifice 

 of this respiratory organ is closed by an opercular appendage 

 (appendice operculaire). This appendage is what 1 have shown 

 to be the gill. 



Moquin-Tandon adds that the orifice is very small. He further 

 speaks of a gland that surrounds the heart, concerning which 

 he says : " The pericardial gland surrounds the heart and the 

 breathing organ, as is the case with most Gastropoda; it occupies 



' Bemerk. ii. d. Bau d. Ancylus, etc., p. 28. 



^ V or (jane respiratoire de V Ancyle n'est, ni un tube ti-acheiform, ni une 

 branchie externa ; c'esL ute poche interieure ; je m'en suis assure, apres 

 de nombieuses dissections, cette poche est petit, oblongue, etroit, et situee 

 a la partie gauche du Molhisque vers le bord du manteau, en avaut du 

 rectum. Recber. anat. physiol. s. 1' Ancyle, etc , p. 123. 



^ Manuel de malacologie et de conch ylogie. Paris, 1825, p. 504. 



