277 



the length of the true operculum. From the abundance of nerve 

 branches in the tip of this pseudoperculum , I am inclined to regard it 

 as sensory in nature. 



The internal anatomy of the European species of sedentary anne- 

 lids has been very completely worked out by Claparède 2 and others, 

 and in the following note I shall describe simply those points in 

 which S. dianthus differs essentially from allied annelids. 



The cuticle covers only the most exposed parts of the body being 

 entirely absent in those portions which are normally protected by the 

 shell. 



In its thickest parts it is made up of several distinct laminae, but 

 exhibits no other internal structure. I could find no trace of cilia on 

 its external surface, as Claparède has figured for allied annelids. 

 Like those , however , it is pierced by numerous channels, the open- 

 ings for the mucous glands. 



The hypoderm covers the whole body, and agrees closely with 

 Souliers 3 description of it in other Serpulae. I could find no trace 

 of »stellar« sub-hypodermal tissue, nor of the «islands« of hypodermal 

 tissue scattered among the muscles, as Claparède has described, and 

 do not think they are present in this annelid. From the appearance 

 of the »sub-hypodermal« layer I am inclined to agree with Soulier 

 that it is transformed connective tissue. 



The muscular, circulatory, and digestive systems, and the connec- 

 tive tissue, peritoneum, and cartilages of the body cavity, agree essen- 

 tially with those of »Spirogr aphis Spallanzani«, as described by Clapa- 

 rède and I need say very little about them here. 



The largest muscles, as stated above, are the longitudinal dorsal 

 muscles, which extend nearly the whole length of the body. They are 

 quite thick, together making up more than half the diameter of the 

 body in its median portions. 



The food of the animal is evidently made up largely, if not enti- 

 rely , of diatoms , as the alimentary canal in all the specimens exami- 

 ned was filled with broken down shells of these minute plants. 



Nervous System. 



The nervous system is quite highly developed, the cerebral gan- 

 glion attaining a diameter of 5 mm in specimens whose whole body 

 diameter was 1,4 mm. This ganglion gives off in front two large 

 branchial nerves, which supply the branchiae, and two smaller nerves 



2 Recherches sur la structure des Annelides sédentaires. Geneva, 1873. 



3 Soulier, Comptes Rendus. T. CVIII. p. 460. 1889. 



