572 DE. H. CHAELTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



ORGANS OF SENSE. 



The bodies most uninistakeably coming under this denomination in the Nematoids 

 are the ocelli so frequently met with in the free species, and of these, almost exclusively 

 in the marine types. As yet I have only encountered a structure of this kind in one 

 land or freshwater species, namely, Monhystera vulgaris. As a rule these bodies 

 are somewhat conical aggregations of reddish-coloured pigment-granules, generally two 

 in number, situated on the dorsal surface of the anterior part of the oesophagus, and 

 exhibiting no refracting portion answering to a cornea or lens, though diffei-ent species 

 may be found to deviate from every one of these common characters, some in one respect 

 and some in another *. Thus in Ebeetii's Enopliis cceruleus they are of a blue colour ; 

 in the genus Enchelidium there is generally one very large pigment-heap almost sur- 

 rounding the oesophagus, of a brownish colour, in the front of which are three or four 

 clear lentil-shaped bodies or lenses; in Phanoderma the pigment-heaps are well-marked, 

 lateral, conical aggregations of bright vermilion-coloured pigment. Where present, in 

 the genus Cyatholaimus they are irregular quadrate masses of a broAvnishyred colour, 

 whilst in the freshwater species above mentioned there is only one small bright-red mass 

 " on the dorsum of the oesophagus. In the genus Leptosomatum there are two conical 

 I masses of red pigment on the dorsum of the oesophagus, each having a single lentil 

 imbedded anteriorly (Plate XXVII. fig. 33). In all the cases just mentioned the pig- 

 ment appears to be situated externally to the sheath of the oesophagus ; but in the genus 

 Enoplus, and in two or three species of Oncholaimus, there seems to be an increased 

 aggregation of pigment-granules into ocelli-like masses in the cervical region of the 

 animal, these aggregations being situated beneath the bounding membrane of the oeso- 

 phagus, within its walls, and being eonstituted of the same kind of pigment-granules 

 that may be found scattered more sparingly throughout the rest of the oesophagus. 

 These internal pigment-heaps I propose to call pseud-ocelli ; they are, doubtless, the 

 early foreshadowings of the more perfect organs ; and accordingly, in one species of the 

 genus Imoplus {E. inermis), I have not found the rudimentary organs similar to 

 those existing in most other species, but what appear to be two distinct pigment- 

 heaps on the external surface of the oesophagus — ^^this organ itself being almost free 

 from scattered pigment-granules. The ocelli are very inconstant organs; they seem 

 present or absent in the same genus according to the requirements of the different 

 species ; thus, in some species of Cyatholaimus living in marine mud they are absent, 

 whilst they are present in other members of the same genus tenanting the smaller 

 weeds of tide pools. 



As before stated no nerve-filaments have ever been actually traced in communication 

 with these ocelli. 



The so-called copulatory papillse in the ventral region of male Ascarides and many 

 other kinds of Nematoids, are I believe principally tactile organs, and I have little 



* Illustrations of these various modifications of the ocelli may be found in Eberth's ' Untersuch. iiber Nemat.,' 

 and also in my " Monograph on the ^jw/ut^MZtt/te," Trajis. of linn. Soc. vol. xxv. 



