INTRODUCTION. 1XXXV 



are in contact with the knot*. These are clearly organs 

 of touch, similar to those which occur in many other 

 animals. Salensky compares their structure to that of 

 the antennae of the Rotifers. 



Closely allied to these sensitive papillae are the tactile 

 tufts, which occur in the articulated avicularia, and which 

 have been already described. In the same category may 

 be placed the bristles which form a line along the back of 

 the tentacles in many species. These are probably analo- 

 gous to the palpocils of the Hydroida, and must largely 

 increase the sensitiveness of the corona, through which 

 the polypide communicates with the outer world. 



An interesting provisional organ has been noticed by 

 Salensky in the young of Loxosoma crassicauda. The 

 arms of the budding polypide are furnished with a very 

 long motionless bristle, placed on the external side, near 

 the top, which disappears at a later stage. He regards it 

 as a tactile organ, needful to the young after its detach- 

 ment, when seeking a site for fixation, but useless to the 

 adult. 



In the larva of Loxosoma Vogt describes an organ 

 composed of two circular hollows, surrounded by a thick 

 border, which forms a kind of bridge between them. 

 Within each depression are placed five or six conical 

 papillae, supporting long cilia, which can be exserted or 

 withdrawn into the hollow. He names it the " spectacle- 

 organ ;" and from its similarity of structure we may infer 

 that it has the same function as the preceding, though it 

 is difficult to determine its precise relation to the economy 

 of the larva. 



* Salensky, " fetudes mir les Bryoxoain."> Kntopruclva," Ann. Sc. Nat. 

 6 e*r. Zool. rol. T. (1877). artu-le no. 3. 



