ON A LITTLR-KNOWN SENSE-ORGAN IN SALPA. 89 



On a Little-known Sense-organ in Salpa. 



By 



Artbur BoUes I^ee, 



Assistant in the Russian Laboratory of Zoology at Viilefranche-sur-Mer 



(Nice). 



With Plate X. 



This organ was mentioned and figured in 1876 by Ussow, 

 in the Memoirs of the Imperial Society of Naturalists of 

 Moscow (T. XVIII, Bd. iii, 2^ Moscow^ 1876). Since then it 

 has not been mentioned by any author, so far as I have been 

 able to discover ; none of the text-books, at any rate, make 

 any allusion to it. Ussow's figure (pi. vii, fig. 49, of the 

 memoir quoted) is very imperfect, missing all of what appear 

 to me to be the most interesting points of the subject. His 

 text is inaccessible to me, being in Russian. I shall do well, 

 I think, to describe the organ as I find it, with only such 

 further reference to the work of the eminent Russian naturalist 

 as may appear useful. 



There are, in Salpa mucronata, two of these organs. 

 They are end-organs of a recurrent twig of the third nerve. 

 They are symmetrically placed, one on either side of the Salp, 

 on the median frontal plane, at a point about halfway between 

 the large muscle that surrounds the anterior orifice of the 

 mantle, and the most anterior of the three muscle-bands that 

 form the well-known cruciform figure on the central region of 

 the animal. Or, in other words, they are situated on the sides 

 of the Salp, on a transverse plane passing somewhat anteriorly 



