10 ARl^HiTR DENDY. 



ectodermal, and on tlie inside by the endodermal layer of 

 muscle-fibres respectively. It is continued into the folds of 

 the muscular layers, and also into the annular fold of endo- 

 derm. It has the usual clear gelatinous appearance,^ and 

 though everywhere more or less distinct, attains its maximum 

 development in the neighbourhood of the tentacle bases, 

 where it appears to become immensely thickened, and at the 

 same time broken up by large vacuoles into a network of 

 irregular sheets (figs. 8, 9). It may possibly be invaded in 

 this region by cells migrating from the endoderm, as will be 

 described later in the case of the supporting membranes of 

 the float ; but this point I have not been able to determine. 



Tentacles of the Proboscis. — The larger tentacles of 

 the proboscis are identical in structure with those of the 

 float, shown in transverse section in fig. 15. The outer wall 

 of the tentacle is formed by a single layer of short columnar 

 cells; it is highly vacuolated, and abundantly charged with 

 thread-cells in all stages of development ; on its inner face is 

 a well-developed single layer of longitudinal muscle-fibres. 

 A more or less distinct layer of mesogloea comes next, crossed 

 in places by slender strands (of protoplasm ?) extending 

 inwards from the ectoderm, while the axis of the tentacle is 

 occupied by an irregular network of sheets continuous with 

 the vacuolated mesogloea of the proboscis wall. Here and 

 there over the surfaces of these thin and apparently structure- 

 less sheets are scattered very well-defined bodies, which may 

 be either small isolated cells with small nuclei, or, as I am 

 inclined to think, themselves large nuclei with conspicuous 

 nucleoli. These bodies are flattened against, or perhaps in 

 the thickness of, the septa which separate the enormous 

 vacuoles from one another. When seen en face they are 

 nearly round, and about 0"0125 mm. in diameter. Their 

 protoplasm stains fairly deeply, especially that of the small 

 enclosed body, and is scarcely at all granular. It is note- 



' It seems probable that, the fibrillated character of tlie niesogla'a described 

 by AUniaii and Miyajima (loc. cit.) in Branch iocerianthus may be due to 

 tlie ectodermal and cudodernud muscle-tibres attached to it. 



