96 



I. IJIMA AND S. IKEDA. 



we have failed to observe epidermal cells. We can not but think that 

 the epidermis had been lost before the specimen was put into the fixing 

 reagent. In the second place, we have determined that it is by a 

 modification of the dermal connective-tissue that the gelatinous tissue, 

 almost similar in its character to that of a Medusa, is formed. We find 

 it traversed in all directions by innumerable, very fine, elastic fibrils, 

 amongst which are sprinkled stroma cells in large numbers. The 

 chromatophores seem to have their seat chiefly in the superficial portion 

 of the layer and also in its deepest part in direct conta,ct with the 

 muscular tunic soon to be mentioned. The same distribution of 

 chromatophores is found in Alloposus pacificus. Here and there in the 

 layer are seen blood-vessels containing blood-corpuscles, fine nerves 

 sending branches to chromatophores and a few branching bundles of 

 fibers which we take for muscular. On the whole it seems the tissue in 

 question closely agrees both in structural and genetical respects with the 

 corresponding tissue of Alloposus mollis as described by Joubin *; only, 

 in Amphitretus the muscles in the gelatinous layer does not show a 

 regular arrangement into definite layers as they seem to do in Alloposus. 



Beneath the thick gelatinous layer and constituting the deeply 

 situated tunic proper of the mantle, there are two thin (about .15 mm. 

 thick) compact-looking sheets of tissues, which are well separated from 

 each other by a layer of a soft and loose consistence. All these can be 

 distinguished by the naked eye on the cut edge of the mantle. 



The outer sheet exhibits on its external surface a number of large, 

 flatly apposed chromatophores. For the rest it is composed of densely 

 arranged muscle-fibers, of which we again distinguish an outer and an 

 inner stratum, composed respectively of longitudinal and transverse 

 fibers. 



The inner sheet is somewhat firmer and again consists of two dense 

 layers of muscular fibers, the outer transverse and the inner longitudinal. 



* Bull. Soc. Zool. de France. T. XX, p. 95. — Unfortunately, Joübin's " Contrib. â 

 l'étude des Céphalopodes de l'Atlantique Nord " in Rés. Se. Camp. Prince Monaco, Fase. 9, 

 does not stand at our disposal for reference. 



