30 GEORGE OSSIAIS SARS. 



Polyzoa they only form a part of the tentacular corona, they 

 represent here the whole lophophore, as it is only on these 

 arms tliat the tentacles have their place. The tentacles in 

 the Rhabdopleura do not form, as in the other Polyzoa, a 

 continuous series, but are interrupted, as well dorsally as 

 ventrally, by an evident interval ; in other words, we have 

 not one single tentacular crown, hut two symmetrical tentacular 

 arms, which take their beginning on each side of the anterior 

 part of the body, and extend out from the same dorsally and 

 diverging to each side. If we examine these tentacular arms 

 in the living animal, we find that they are also in many re 

 spects different from the lophophore of the Hippocrepia. 

 While the latter always retain unchanged their form and 

 somewhat inclined direction, the tentacular arms in Rhab- 

 dopleura are in a high degree flexible and variable in their 

 direction relatively to the body of the polypide and to 

 each other. As long as the polypide is withdrawn into 

 the cell, they are always extended straight forward and 

 nearly parallel with each other, forming, together with the 

 tentacles attached to them, a close fascicle extending in the 

 same line with the body. As soon as the polypide reaches 

 the aperture of the cell, they spread out from each other, but 

 this takes place in various manners. Sometimes they are 

 bent with the ends only a little out from each other, while 

 otherwise they are nearly parallel (see fig. 5) ; sometimes 

 they spread themselves out so widely on each side that 

 they stand almost diametrically opposite; sometimes they 

 bend themselves with the ends downwards (see fig. 5) ; some- 

 times — and this is most usual, and always occurs when the 

 animal is taken out of its tube — they are bent upwards 

 and backwards, and that often so strongly that they describe 

 a nearly semicircular curve, so that the extremities even 

 touch the dorsal side of the polypide's body (fig. 1). This 

 great mobility of the tentacular arms or lophophore (so 

 different from what is observed in the other Polyzoa), which 

 appears to be produced at will by the animal, sometimes in 

 one manner and sometimes in another, must certainly, 

 although it always takes place very slowly and with little 

 energy, be brought about by means of auxiliary muscles or 

 muscular tissue. I have, however, only succeeded in observ- 

 ing very faint traces of anything of the kind. When the 

 animal is gently compressed between two glass plates, one 

 may observe on each side some very fine fibres (figs. 1 and 2, 

 p) passing obliquely over the gullet, proceeding from the 

 ventral side, where the body of the polypide forms on each 

 side a small conical prominence (ibid., o, o), which may per- 



