Defence among certain Medusce. 345 



bell of genera like Gemmaria and Willia. In Atlioryhia 

 also the rows of so-called nematocysts on the outer walls of 

 the covering-scales do not in many cases show the " fil d'un 

 nematocyste," and therefore we may well question whether 

 tliey are functionally nematocysts, lacking as they do this 

 characteristic internal organization of these organs. Still the 

 homology of these structures with nematocysts is an open 

 question, and it remains yet to be seen whether they might not 

 be regarded as lasso-cells in which certain parts have suffered 

 a change in form. 



There seems nothing to prevent our accepting the theory 

 that the " corps spheriques " of the above description are 

 homologues of nematocysts, and Bedot's figure, as far as it 

 goes, does not disprove that they are these organs even if the 

 central " thread " is absent. 



Between these spherical bodies, however, and the pigment- 

 pouches or glands Bedot thinks it necessary to recognize a 

 distinction, and certainly their form is very diiferent and 

 justifies his views in this regard. Moreover the pigment- 

 glands discharge their contents, whereas the spherical bodies 

 do not have this power. Is there, however, anything to show 

 that the pigment-glands are not more completely developed 

 clusters of the so-called spherical bodies? and may not the 

 pigment-gland be formed by an aggregation and maturation 

 of the spherical bodies ? Such an interpretation was given 

 the coloured bodies when I studied them, and there is no new 

 evidence to lead me to abandon my former opinion. The 

 " pigment-spots " were at that time regarded as remotely 

 represented in Apolemia " by elevations composed of clusters 

 of cells on the surface of the tract." My use of the word cell 

 with two meanings, one as a lasso-cell and the other as a 

 histological cell, has led to a confusion and a just criticism 

 by Bedot. I consider the pigment-glands to be formed of an 

 aggregation of nucleated cells, and each pigment-spot to be 

 comparable to a nematocyst (lasso-cell). 



In some genera irritation of the animal leads to a change 

 in colour of the covering-scale, which may be akin to the 

 discharge of pigment from these bodies. This phenomenon 

 seems also to be connected with pigment-cells in the organs, 

 although the character of these structures has not been fully 

 described. 



Dr. Carl Chun mentions a change of colour of the covering- 

 scales in Ceratoci/inha spectahilis from the Canaries. He 

 speaks of this phenomenon in the following manner : — 



" Sehr eigenthiimlich verhalt sich das Deckstiick bei 

 starkerer Beriihrung, insofern auf eiuen Reiz hiii zuerst in der 



