624 



coelom; in my own work on A.fragilis I believed that 1 traced it into 

 connection with blood sinuses and therefore interpreted it as a part of 

 the primary body cavity or haemocoele. While I am not now prepared 

 to say with certainty whether it is a haemocoele or a coelom, I ain 

 convinced that Haller's observations are incorrect. What he considers 

 the right half of the coelom is an undoubted part of the nephridium 

 as shown by the epithelium. The space now in question shows no 

 trace of an epithelium of this sort. Furthermore in A. tesiudinalis the 

 space is not restricted to the left side of the body but extends for a 

 considerable distance to the right, lying between the nephridium and 

 the viscera. 



Subradular organ. Finally H all er has affirmed the existence of 

 a subradular organ in various Docoglossa, while the statement has 

 been categorically denied by Thiele, whose observations have received 

 general credence. For a summary of the existing state of opinion see 

 Simroth's edition of Bronn's Mollusca, Abth. Gasteropoda, p. 321. 

 It is therefore with pleasure that I have discovered what I believe to 

 be Haller's subradular organ, though the pleasure is tempered with 

 regret since I must add that in my own earlier work on A. fragilis 

 I entirely failed to appreciate the nature of the structure and did not 

 even describe it. 



The subradular organ is a somewhat cushionlike projection from 

 the under side of the odontophore just behind the tip of the radula. 

 It is divided by a V-shaped groove into an anterior and a posterior 

 part both of which are clothed with long columnar epithelial cells. In 

 the posterior part only have I been able to make out any differentiation 

 of cells; here, intermixed with the common epithelium which appears 

 to be ciliated, though I can not be quite sure of this, are fusiform cells 

 which have much the appearance of sense cells. I have not as yet 

 made out the innervation of this organ; I may however say with assu- 

 rance that no compact ganglion lies Avithiu it. The subepidermal mass 

 consists of connective tissue traversed by irregularly arranged muscle 

 fibres. 



Until a complete study has been made of both epithelium and 

 innervation, it is impossible to say whether this is to be interpreted as 

 a vestigial organ or as one which is still functionally active. 



Since reading the paper of which the above is an abstract I have 

 found two preserved specimens in which the odontophore was pro- 

 truded from the mouth and the radula so retracted that the subradular 

 organ formed the tip of the odontophore. Whether this was an arte- 

 fact remains to be determined. 



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