oj- the Bay of Naples. 103 



that the differentiation into nearly smooth and thin, and into 

 finely granular thick vessels, certainly indicates such a 

 division of labour. The water- vascular system of Sei'son, so 

 far as one can judge from the extant investigations, is not 

 quite so developed as in our animal. There is said to be only 

 one flicker-organ, which represents that indicated by me as 

 z^, and in the trunk only one wide canal, which latter, 

 " ascending to the intestine," passes into " a delicately mem- 

 branous saccule lying upon this." 



The connective tissue is represented in Paraseison by a few 

 thin threads, which extend between the organs and the skin. 

 Of the animal organs. 



The nervous system has become very little known to me. 

 Above the anterior extremity of the oesophagus there is in the 

 head an elongated organ, somewhat pointed in front and ter- 

 minating broadly behind, the hrain (fig. 6,^), in which, by 

 means of reagents, the presence of numerous nuclei with 

 comparatively large nucleoli may be demonstrated. This 

 is connected posteriorly with a dorsal feeler (fig. Q, d.t), the 

 setj» of which arise from a circular aperture in the skin. 

 Their size is very variable in difi!"erent individuals ; frequently 

 they are very long and easily recognizable, while in other 

 individuals they are remarkable for their smallness. To the 

 nervous system, no doubt, belong also the four groups of 

 tactile setge (figs. 5, 6, t) which surround the buccal aperture ; 

 but I was unable to ascertain their connexion with the brain. 

 Lateral feelers, which are so characteristic of the freshwater 

 Rotatoria with the exception of the Philodlnasa, are wanting 

 in Paraseison. No eye-spots were seen. 



The muscular system is difiicult to observe in its details, 

 owing to the constant mobility of the living animal. The 

 longitudinal musculature is especially developed ; whilst of the 

 scantily developed transverse bands we need mention only 

 three tolerably broad muscles, which lie at equal distances 

 apart below the dorsal surface of the trunk and extend over 

 the dorsal half of the sides of this division. The system o 

 thin transverse muscles covering the whole ventral side of the 

 trunk, Avhich is so characteristic of Seison, is entirely deficient 

 in Paraseison asplanchnus. 



Of the longitudinal muscles those are of course the most 

 important which, on the one hand, retract the neck into the 

 trunk and, on the other, the hindmost segments Into the basal 

 part of the tail. During invagination the neck always comes 

 to lie near the ventral surface, below the stomach, as the muscles 

 which act in this operation are nearer to the lower surface of 

 the body than to the back. These are two strong bands 



