HIPPOLYTE VARIANS. 607 



either to those of the segmentally arranged vessels supplying 

 the swimraerets and coming off in pairs from the dorsal aorta, 

 or to branches of these which divide in the connective 

 tissue under the skin of the pleura (PL 34, figs. 14 — 16). 



The best example of this close relation between the pig- 

 ment and the blood is seen in the eye-stalk (PI. 34, figs. 17, 18). 

 Within the eye-stalk lie the optic ganglia enclosed in con- 

 nective tissue. Between the ganglia are the bodies of two or 

 more large dark red pigment spots, whose processes extend 

 right and left, at right angles to the narrower elongated 

 centres, in a peculiar paired fashion over the ganglia. The 

 blood is carried by an artery which runs near the surface of 

 the eye-stalk, and which, after bifurcating, divides into a large 

 niimber of bi'anches interdigitating with the pigmented pro- 

 cesses of the " chromatophores " (PI. 34, figs. 18, 19). 



Previous observers of these Crustacea do not appear to have 

 noticed the abundant store of chromatophoric pigment which 

 exists in the muscles of Hippolyte, especially in the ex- 

 tensors and flexors of the tail. In these positions the 

 " chromatophores " are so abundant that if, for example, a 

 piece of muscle is cut out of a pink prawn, the muscle itself 

 is seen to be pink, and under the microscope the arrangement 

 of the pigment is similar to that of PI. 34, fig. 20. The trans- 

 parent or semi-transparent specimens of Hippolyte (par- 

 ticularly the immature and male examples) owe such colour 

 or pattern as they possess more to these " muscle-chromato- 

 phores" than to the dermal ones underlying the skin. In 

 larger and more opaque forms the colour is determined 

 rather by a superficial network formed by the dermal 

 " chromatophores," which thus hide the (often similarly 

 coloured) intermuscular ones (PL 35, fig. 24). 



The presence of pigment distributed in " chromatophores " 

 among the muscles is by no means peculiar to Hippolyte 

 varians. In the true prawns (Pala3mon serratus) the 

 stripes of colour are due to superficial "chromatophores" in 

 the skin, each containing red and yellow pigment surrounded 

 by a little blue. In the depths of the tail muscles there is 



