620 



CILIA. 



in one of them, the D. cornuta, the ciliary 

 motion was very strong on the club-shaped 

 feelers; perhaps it may be the same in all. 

 I also examined the Tritonia and Eolis belong- 

 ing to this order, and found the ciliary motion 

 in corresponding parts. 



b. Cyclobranchiata. In the Patella or 

 Limpet (fg. 302, representing the under 

 surface), the gills form a series of simple 



Fig. 302. 



on each side of it, Fig. 303. 



diminishing in size 



as they approach its 



point. The currents 



on each of the gills 



are directed towards 



its apex, and also 



pass between the 



secondary laminae 



over their surface 



and along their 



edges : a, a, are the 



gills ; b one of the 



gills magnified, 



showing its laminae ; Chiton. 



c the same viewed 



endwise. The arrows mark the direction of 



the currents. 



c. Pectinibranchiata. The common Buc- 

 cinum (Jig. 304) may serve as an example of 



Fig. 304. 



Patella. 



B. Portion inclosed between the lines c and d, 

 magnified to show a, a, the branchial la- 

 minae, and b, b, the circular border of the 

 mantle. 



laminae (#, a) attached within the circular 

 border of the mantle (b, b}. The currents pass 

 inwards from the edge of the mantle to the 

 gills, then over the surface and along the border 

 of each branchial lamina, from its outer or 

 lower to its inner or upper edge, as indicated 

 in the figure by the arrows. In the Limpet 

 the ciliary motion is also found on the inner 

 surface of the alimentary canal. 



In the Chiton or Oscabrion (Jig. 303), the 

 only other genus of this order, the gills are 

 situated as in the Limpet, but are of a more 

 complex structure. Each consists (at least in 

 the species examined by me) of a triangular 

 lamina, with a series of smaller laminae set 



Buccinum Undatum. 



this order. The gills, as accurately described 

 by Cuvier, are attached to the roof of a bran- 

 chial cavity or recess formed between the man- 

 tle (, a) and upper part of the body (6) in the 

 last turn of the shell, and opening anteriorly 

 by a broad slit. At the left end of the slit the 

 edge of the mantle is prolonged in the form 

 of a groove (c), which prolongation is called 

 the syphon, and is lodged in a corresponding 

 groove of the shell. On detaching the roof 

 of the branchial cavity at the left side, and 

 reflecting it (as represented in the figure), we 

 find attached to it, first, the gills, consisting 

 of a short double row (d) and a longer single 

 row (e) of laminae, the latter being larger ; 

 secondly, to the right of the gills, the so-named 

 mucous laminae (/,./); thirdly, still more to 

 the right, the rectum (g). 



The water enters by the syphon, and issues 

 at the right extremity of the branchial slit. 

 The ciliary motion and currents take place on 

 the gills, mucous laminae, and rectum, and on 



