HIPPOLYTE VARIANS. 609 



fusion of the brandies of one chromatophore with those of 

 others. On one point, the histological character of these 

 colour elements, our evidence is incomplete. We have not 

 been able to demonstrate that the pigment spots or " chro- 

 matophores " are " cells." In most cases the pigment 

 appears to be stored in connective-tissue lacunae. On the 

 other hand, the flowing movement of the pigment to and 

 from a " centre " seems only explicable on the view that 

 these bodies are really cellular. We may point to the 

 recent work by Holmgren and Schreiber on the crayfish and 

 prawn for evidence on this head. 



Holmgren has shown (1898, p. 409) that in the prawn 

 (Palsemon) the chromatophores are nucleated connective- 

 tissue cells the processes of which are frequently confluent. 

 Both authors describe a peripheral nerve-plexus in close con- 

 nection with the colour elements and the ordinary nerve-trunks. 



So far we have dealt only with the most prevalent kind of 

 " chromatophores," but there is another element to which we 

 must briefly refer. At the bases of abdominal pleura, along 

 the mid-dorsal line, on the eye-stalks, and in few other 

 positions a colour element occurs which possesses fine branches 

 radiating from a well-marked central body. By transmitted 

 light these spots are almost invisible to the naked eye, whilst 

 under the microscope they look yellowish or dull greyish 

 green. By reflected light they are brilliant yellow, more 

 brilliant indeed than the yellow of the ordinary chromato- 

 phores. They are filled with minute granules (often 1 ^ in 

 diameter), together with a small amount of homogeneous 

 yellow pigment. Similar colour elements are of constant 

 occurrence in allied Crustacea. 



Leaving the red-lined variety and turning to the brown 

 colour form ofHippolytevarians, we encounter an arrange- 

 ment different from that just described. Under the micro- 

 scope the colour is seen to be due to a dense red network 

 enmeshing the clear cells of the epidermis, and blotched here 

 and there by green patches (PI. 35, fig. 24). Some patches, 

 bolder than the rest, seem to indicate the position of the 



