STRUC'l'URE AND DEVELUl'MENT OF COEEOPLANA. 17 



T e )i t a c 71 1 a r Ap p aratus. 



The tentacular apparatus of Cocloplaiia is largely of the same 

 structure as that of the cydippid ctenophores. Two apparatuses make a 

 pair and ate placed in the transverse plane, one on either side of the 

 sagittal axis of the body. The tantacle itself is an extremely contractile 

 filamentous organ with numerous accessor}' branches arranged at regular 

 intervals on it throughout its length. When fully extended, it may be 

 more than twenty times as long as the diameter of the body in a 

 moderately distended state and it can be withdrawn into a sheath formed 

 by a caecal depression of the body surface. The proximal end of the 

 tentacle is enlarged into a root-like structure called the tentacle-basis, and 

 is attached to the wall of the sheath. 



In all typical cydippid ctenophores (PI. 2, fig. 3), the tentacle-sheath 

 and the tentacle-basis lie nearly vertically, parallel with the main axis 

 of the body, and the tentacle-sheath may be divided into two parts, 

 one elongate vertically containing the tentacle-basis and the other set 

 more or less oblique accomodating the tentacle-stem. These two parts 

 of the tentacle-sheath are well represented in Coeloplana too (PI. 2, fig. 

 4; PI. 3, fig. 8), but they are both disposed horizontally, the part accom- 

 modating the stem directly on the roof of the part occupied by the 

 basis; the entire sheath accordingly makes a sharp bent between those 

 two parts. For the sake of description, I shall hereafter call these two 

 parts of the tentacle-sheath one, the dorsal, and the other, the ventral 

 compartment {t. sh. d\ t. sh. v). More precise situation and configuration 

 of the tentacle-sheath may be understood by PL !i, fig. 2. 



The ventral compartment (PI. 2, fig. 2; PL 3, figs. 1-8; /. sh. i)) 

 takes precisely the shape of the tentacle-basis which it encloses. In the 

 dorsi-ventral view, the compartment is divided, though not very definitely, 

 into three parts, viz. a relatively narrow median part lying in the 

 transverse plane of the body and a pair of somewhat broader lateral 

 parts placed on either side of the former. The dorsal compartment {t. 

 sh. d) is flask-like in shape and provided with a conspicuous lateral 

 outbulging on either side of its base. Moreover, it sends out towards 

 the centre of the body a pair of small horn-like processes. The two 

 compartments are communicated with each other near the proximal end 

 by a relatively narrow median passage. With regard to the tentacle- 

 sheath, Abbott maintains: "Lying normally below the main cavity of 

 the sheath, but sometimes pushed to one side, is what may be called 



