t8 T. KOMAI: STUDIES ON TWO ABERRANT CTENOITIORES 



the accessory sheath The tentacle itself may be said 



to be anchored to the whole floor of this accessory sheath which spreads 

 out into a broad flat cavity and is lined with formative tissue" ('07, p. 

 55). Evidently, the accessory sheath referred to is nothing but the ventral 

 compartment of the sheath, therefore, not a characteristic structure of 

 this animal, being found in all cydippid ctenophores too. 



The tentacle-sheath is lined with a low epithelium of the ectoderm- 

 al origin and is beset with cilia all over its surface. The cilia are 

 rather short and stiff, especially those which are found in the distal parts 

 of the dorsal compartment. The two kinds of gland cells occurring in 

 the epidermis are also met with here, though much rarer than the 

 ciliated cells. They arc usually larger in size than the latter, bulging 

 out above and below the level of the epithelium. According to Abbott 

 ('07), the tentacle-sheath should be lined with endodermal cells in certain 

 places, and the cells are said to proliferate by budding, giving rise to a 

 kind of free cells of phagocytic function. It is highly probable that, the 

 alleged endodermal cells are nothing else than the cells on the dorsal side 

 of the tentacular canal, which are generally of enormous size and show a 

 quantity of inclusions, besides, colloblasts are found among the inclusions 

 rather commonly. It is not impossible that, the cells with such inclusions, 

 especially those having colloblasts within, should be taken for phagocytes, 

 although they are fundamentally different from them of course. 



The tentacle-basis occupies the whole floor of the ventral compart- 

 ment of the sheath and is situated quite horizontall\\ To bring about 

 this peculiar disposition, the basis makes a turning of ninty degrees at a 

 certain stage of development of the animal from the original vertical 

 situation to the new horizontal one. The proximal end of the basis in 

 this new situation is homologous with the original aboral end, and the 

 distal end with the original oral end. Though peculiar is the disposition, 

 the tentacle-basis does not show any deviation from that of cydippid 

 ctenophores with respect to structure. It is made up of embryonal 

 tissues in various developmental stages of the component parts of the 

 tentacle. It consists of two distinct parts, one which gives rise to the 

 muscular core of the tcntacle-stcm as well as of the accessory filaments 

 (PI. 2, figs. 2, 4; PI. 3, figs. 3-6, 8; /. r) and the other, from which the 

 epithelial parts of the same are derived (/a cp). I propose to call the 

 former the tentacle-root and the latter the basis-epithelium. 



In the total view, the entire tentacle-basis presents itself as a 

 shield-shaped structure which consists of three distinct parts l}'ing along 



