328 Dr. Williams on the Mechanism of Aquatic Respiration. 



a broad single column (fig. 7, arrows). It is then suddenly 

 deflected forwards into the interior of the gills (e), which, in 

 Octopus and Sepia, form hollow conical organs, in Loligo and 

 the C5alamary a hollow semicy Under. In the former during the 

 moment of inspiration a copious column of water rushes up 

 the hollow axis of the gill ; in the latter families, along the 

 inferior concavity. These currents are directed by a most 

 complexly coordinated series of muscular actions. From the 

 interior of the branchiae the water is compressed by a muscular 

 power resident in the branchiae themselves. It issues in as 

 many streams as there are perforations between the ultimate 

 pinna of the organ. These streams regather themselves and 

 flow backwards again in the direction of the base of the gills, 

 leaving the branchial hearts and other large blood-channels 

 situated in that region ; then driven forwards by the expiratory 

 collapse of the entire mantle, the water in form of a single 

 column enters the base of the funnel (/), through which it 

 finally leaves the cavity as an excretory and expiratory cur- 

 rent (a). 



The author will explain on another occasion how much that 

 is old and how much that is new is contained in these observa- 

 tions. In succeeding papers they will be supported by a large 

 mass of anatomical details of great interest, and hitherto, he, 

 believes, unknown to naturalists. , , 



"■' ^^ mPLANATION OF PLATE IX. 



,^«AJJ faJLM 

 Fig. 1. An imaginary vertical section through the shell and body oi Patella 

 athletica. a, water-cavity in the roof of the shell, capable of 

 being enlarged to the dimensions of b and c. e, gills ; /, fringed 

 fi JbfiSlOedge of the mantle ; ff, g, edge of shell ; i, foot j j, anus, termi- 

 nating in the chamber above the mouth. 

 Fig,. 2.,^ longitudinal section of the shell of Buccinum undatum, showing 

 .the abdominal spires, a, a, a, a, which are filled with water and 

 g'iiB<| ^^tvith the abdomen of the animal, b. denotes the ligament by^ 

 -'lJi8 19'which the animal is attached to the columella, c. > 



F^g*^ 3 A. Male animal of Buccinum undatum taken out of its shell. At 

 ^ J , , b. is shown the mode in which the penis is carried in the branchial 



\, , , chamber a. 

 Fi^y 3 B. The same animal with the penis withdrawn from the branchial 



gyiiic; L- chamber. On the left is the siphon through which, as indicated ^ 

 / 89^9 9iiby the arrows, the water enters the chamber («), describing therein ^ 

 rttiw ^'^ circuit marked by the arrows ; it escapes at the right cleft b. ' 

 Fia^A.,;the animal of Lymneus stagnalis taken out of its shell. The 

 /' '^^ arrows define the pulmonary chamber and the circulation pcy- 

 iBJflOl. formed by the air under the vermicular action of the walls, b. isj, 

 JfiDlilOthe posterior limit of the thoracic chamber; c. marks the solid 

 sbig 'I abdominal portion of the ho^yi '^^' d}\\ii j^piratory and defe-j' 

 ' Y-ttrrifi^^^^^^^'y siphon. . iHlu) .tiuil-^ v* 



jfeo. ,i,r?waa: m«a;iw«A" in outhnc. «. deflptes. ;tUe respiratory and defe- 



