THE GEPHYREA OF JAPAN. 67 



Inspite of its external resemblance, however, this species 

 differs remarkably from Thalassema mucosum in internal anatomy. 

 In this resj)ect it shows, contrary to expectation, an essential 

 agreement with Thalassema elegans. Indeed, the agreement may 

 be said to be complete, the only difference being that all the 

 visceral organs in the present species are developed on a smaller 

 scale in proportion to the smaller size of its body. It therefore 

 seems unnecessary to give a description of the anatomy. How- 

 ever, certain points with regard to the segmental organs of the 

 species require special mention. In the females, the said organs 

 as far as they have come under my observation, are invariably 

 present in three pairs, all situated behind the ventral hooks. 

 On the other hand, the males show these organs in varying 

 numbers and arrangement, a fact which seems to be of interest 

 in relation to the polynephridism I have observed in T. 

 tcenioides and T. elegans. In one male specimen of the species 

 I have found them in eight groups arranged pairwise, each 

 group consisting of four organs, making thirty-two in all. 

 In some other male individuals, the organs were present in 

 three paired groups, some of which comprised four and 

 others only one or two organs. As to the shape of the organs 

 in question, there exists scarcely any difference from those of 

 T. elegans. 



Habitat : I have found the species very common in the 

 shallow waters around the islet of Gogoshima (Province of lyo). 

 The presence of the worms is indicated by the large and pecu- 

 liarly shaped faecal masses scattered around small elevations of 

 the bottom exposed at low tide. Lately I was presented by 

 Mr. Izuka with a specimen of this species which he obtained 

 in the inlet of Moroiso near the JMisaki Marine Laboratory. 



