THE STRUCTURE OP XENIA HICKSONI. 199 



one case the process, which is a very large one, bears a short branch 

 near the middle of its length (Fig. 25, B). This is the only branched 

 process found among many hundreds examined. The processes of most 

 of the cells project outwards almost at right angles to the free surface 

 of the endoderm (Figs. 20, 21, 23, 24), but there are many similar 

 to the one drawn in Fig. 22, in which the process is strongly curved 

 and apparently moderately flexible. 



These curious processes are very numerous, and are found in all 

 parts of the endoderm lining the coelenteron and tentacles, but are 

 most abundant in the portion of the coelenteron situated in the body of 

 the polyp and in the upper part of the stem (PI. XX., Fig. 9). 



The nature of these processes is difficult to determine. In the pre- 

 liminary note to the Royal Society (1898, written in February) I called 

 them pseudopodia, but further investigation shows that the word flagella 

 would probably better express their nature. The processes appear to 

 be permanent, to have a moderately definite shape gradually tapering 

 from base to tip, and to be flexible. The word pseudopodia implies more 

 temporary structures with many different and continually changing 

 shapes, while the term flagella implies tapering whiplash-like processes 

 of more permanent and definite shape. The homogeneous structure of 

 the greater portion of these processes, differing so markedly from the 

 vacuolated granular protoplasm of the rest of the cell, is also more in 

 accord with their being flagella, as pseudopodia have the same structure 

 as the body of the cell from which they are protruded. 



It is difficult to suggest the probable function of these giant flagella. 

 They are evidently motile organs, as they may be found in all stages 

 of flexion, some being practically straight, while others are bent almost 

 into a semicircle. Their action probably serves to keep the liquid in 

 the coelenteron in slow motion, thereby securing a more equal distribu- 

 tion of the nutrient substances contained therein to the cells in their 

 vicinity. 



Many of the endoderm cells are provided with " muscle processes," 

 but these processes are not numerous in the pinnules and in the stem ; 

 they are more numerous in the endoderm of the tentacles and of the 

 free portion of the polyp. The muscle-fibres (except those forming the 

 retractors and protractors) have a circular direction, and are similar to 

 those of Alcyonium. In Alcyonium, however, the endoderm cells of the 

 tentacles do not possess muscle-fibres (Hickson, 1895, p. 376). 



