53 



Perichaeta. In my opinion however, the supposed homology is not 

 well founded, as the epidermis-organs of Pontoscolex do not show 

 much resemblance neither in their situation, nor in their appearance 

 with the bristle-cells of Anachaeta; the latter ones are large, glandular 

 cells, which are not entirely embedded in the epidermis, but extend 

 themselves at a distance into the body-cavity. Moreover it is clear , that 

 a body lying in the circle of the setae , may not only for this reason be con- 

 sidered to be homologue with them. Beddard at first describing the 

 epidermal structures, found in Eudrilus , considered them as representing 

 rudimentary setae, afterwards however reexamining them in Hyperiodri- 

 lus and Heliodrilus l ) he came to the opinion , that they must rather be 

 regarded as of a sensory nature , which view nearly at the same time was 

 put forward bv myself with regard to those bodies in Eudrilus 8 ). The 

 sensory bodies of Lumbricus , according to the investigations of Cerfon- 

 taine 3 ), are also in many segments specially to be found in the ele- 

 vated zone of the bristles , so being , in his opinion , far better situated 

 for their sensory function. I observed that in much contracted spe- 

 cimens of Pontoscolex , the bristle-zone of the anterior segments 

 also has the appearance of an elevated ridge. Though the finer structure 

 of the epidermis-bodies of Pontoscolex is not sufficiently known, it 

 seems to me more probable , that they too are of a sensory nature. 



The different authors, who examined P. corethrurus, are not quite 

 in agreement about the structure of the cephalic extremity of this 

 worm. Fritz Müller *) says , that if the worm protudes the cephalic 

 extremity, from out the first segment one or two other segments 

 come in sight, besides a long-stalked, club-shaped cephalic lobe. 

 Perrier on the contrary states , that the cephalic lobe is totally absent, 

 that the mouth is terminal and surrounded by the buccal segment , 

 which is devoid of bristles ; but that in front of this, another segment 

 without bristles exists, and that both can be inverted. Rosa rightly 

 pointed out, that if Perrier's view were right, all organs in Pontos- 

 colex would lie one segment more backward than in other Lumbrici- 

 dae; but as this suggestion is not very probable, he believes the 

 segment, which Perrier calls the first, to be the everted portion of 



1) Quartl. Journ. Microso. Science, Vol. XXXII, 1891, p. 235. 



2) Mem. Soc. Zool. de France, Vol. Ill, 1890, p. 1, pi. VIII. 



3) Archives de Biologie, T. X, 1890, p. 363. 



4) Archiv, f. Naturgeschichte, Jhrg. XXIII, 1857. p. 113. 



