loxosoma, 357 



Organs of Sense. 



On each side of the body, placed somewhat on the dorsal 

 aspect and on a level with the enlarged portion of the intestine 

 (the rectum), is a papillary eminence [d, PL XXII, fig. 11), 

 from which rise a number of short, somewhat rigid bristles. The 

 cuticle is continued over the. papilla, but is attenuated towards 

 its summit. In the interior a number of elongated, conical, con- 

 verging cells are visible, with the pointed extremity directed 

 upwards, and apparently in direct communication with the 

 bristles, which rise from the papilla. These bristles are acumi- 

 nate, and appear to be slightly flexible, but exhibit no move- 

 ments of their own. 



The papilla, on the contrary, are eminently contractile; they 

 shrink into themselves ; the summit is drawn inwards, leaving a 

 crater-like depression, in which the bristles are concealed, and 

 ■when the contraction reaches its extreme point nothing is visible 

 but an insignificant rising of the skin without any trace of spe- 

 cial structure. The papilla are present on the buds in the later 

 stages of their development, before their separation from the 

 parent, and on the two sexes alike. The contained cells, like 

 those which compose the hypodermic layer, are finely granulated 

 and without any apparent nucleus. 



As to the significance of these bodies, they resemble in structure 

 the tactile or sensitiwe papilla, which occur in so many animals, 

 and have, no doubt, a similar function.' A difficulty indeed lies 

 in the way of this interpretation, from the fact that no observer 

 has yet detected any trace of a nervous system. The author has 

 sometimes fancied that he could make out lines, as it were, 

 radiating from the papilla towards the middle of the body, but 

 there was so little definiteness about them that it was impossible 

 to draw them, and they might, with equal probability, be taken 

 as indications of superficial wrinklings in the cuticle. However 

 this may be, the existence of these structures, so evidently tactile 

 in their nature, seems to lead almost of necessity to the conclu- 

 sion that a nervous system must exist, perhaps similar to that 

 discovered by Nitsche in Pedicellina, and of which that author 

 considers he has found some indistinct traces in Loxosoma. 



' The papilla of Loxosoma bear a close geueral resemblance to the tac- 

 tile organs wliich occur on the tentacles of the Hydroida, and which were 

 first described by Dr. Strethill Wright as pcdpocils. I am not aware that 

 any similar structure has hitlierto been noticed amongst the Polyzoa, with 

 the exception of the tuft of setts or sensitive hairs that is met with be- 

 tween the jaws of the aviculariuui in some of the Cheilostomatous forms; 

 unless, indeed, the extremely delicate setiform processes ranged along the 

 back of the tentacles in some species must be placed in the same category. 

 — Transl. 



