NOTES ON THE ANATOMY OF DINOPHILUS. 45 



in the description of the specific characters, is dependent on the con- 

 dition of the connective-tissue cells. 



Each nephridium (of the first four pairs) 'consists of three por- 

 tions : (i) the ciliated appendage ; (ii) the excretory portion ; (iii) 

 the duct. The entire nephridium is almost certainly composed of a 

 small number of perforated cells, although no nuclei were discovered : 

 it forms a moderately short tube, without convolutions, the curvature 

 of the tube, as actually observed, doubtless depending to some extent 

 on the position of the animal in the compressorium. Thus the dif- 

 ferences between the nephridia of the two sides in fig. 15* probably 

 imply nothing more than that the direction of the compression was 

 not the same in 'all the observations made. 



The excretory portion of the nephridium is of a distinct greenish- 

 yellow or orange colour, the walls of this portion of the tube contain- 

 ing numerous colourless vacuoles, and granules of various sizes. 

 One or two of the granules are very frequently large and deep orange 

 in colour. The excretory portion is pear-shaped, the narrow end 

 shading ofE insensibly, by gradual loss of the vacuoles and granules, 

 into the duct. The first nephridia seem to be usually provided with 

 two swollen portions, whose walls contain excretory granules and 

 vacuoles, instead of with one only, as in the case of the remaining 

 excretory organs. The nephridium is often suspended in a cord of 

 the above-mentioned pigmented connective-tissue cells. 



The internal end of the nephridium is composed of a triangular, 

 ciliated appendage, the apex of which is inserted into the excretory 

 portion of the tube. This insertion, in the case of the second, third, 

 and fourth nephridia, takes place at some little distance from the 

 proximal end of the excretory portion. The appendage is ciliated, 

 the cilia together giving the appearance of a pointed flame-like 

 structure which projects obliquely into the excretory portion of the 

 organ. In certain conditions of the nephridium the ciliated appen- 

 dage has exactly the appearance of a flame-cell, although as the 

 animal dies and the cilia become more sluggish in their movements, 

 the flame-like appearance is lost. I am inclined to believe, as the 

 result of a long series of observations, that the appendage is pro- 

 vided with a number of cilia, which, working together, produce the 

 optical illusion of a vibratile flame. This is almost certainly true of 

 the portion of the tube described above as the duct, this region being 

 undoubtedly lined by cilia, which, under certain conditions, give rise 

 to a very flame-like effect. 



In spite of having devoted a large amount of time to the observa- 

 tion of the ciliated appendages, I am unable to say whether or not 



• The form of each nephridium representing the result of one or more actual observa- 

 tions, made at different times. 



