HIPPOLYTE VABIANS. 653 



Appendix. Experimental Tables. 

 Idst of Abbreviations. 



Colours. — Since each of the terms brown, blue, green, red, covers such a 

 wide range of colour, it is necessary to define more exactly what we mean by 

 them. By brown is meant the colour of the brown seaweeds (Pucus, 

 Halidrys, or Laminaria) ; by green, emerald green (of Zostera); by 

 red, a claret colour ; by blue, various shades of indigo. Yellow (when seen 

 by transmitted light) is a straw-colour, but by reflected light yellow is the 

 most brilliant Indian yellow. By this illumination " frosted effects " are 

 often recorded. By this term we mean a bright almost sparkling colour, 

 suggesting a reflecting substance. The yellow, whitish, and blue markings 

 (invariably quite on the surface of the skin) are of this kind. By transmitted 

 light such markings are dull and greyish. 



Topographical Terms. — The body of Hippolyte varians has a hump in 

 the middle of its back or tail. As this point of flexure is often distinctively 

 coloured some term is necessary, and " hump " has the merit of being clear 

 and short. The two flat scissor-like blades of the antennae are spoken of as 

 the " antennal scales." As the body is frequently of one tint in the middle 

 region (usually from the stomach to the hump), and of another in front of 

 and behind this central portion, we speak of the "Mid," "Ant.," and 

 " Hind." 



Ground Colour. — Apart from the obvious " chromatophores " the body fre- 

 quently appears to possess a ground colour possibly due to diffused pigment, 

 possibly to very fine chromatophoric branches. 



Chromatophores. — The apparent form of these bodies alters as the pigments 

 flow outwards from the centre or retreat towards it. When the pigments are 

 maximally contracted they form irregular masses of one or more colour, and 

 the chromatophores may then be described as " contracted," though the term 

 applies rather to the pigment than to the chromatophore, the actual form of 

 which is probably unaltered. In this condition the pigments (by reflected light) 

 often show what look like "coloured vacuoles " (see supra, p. 626), the nature 

 of which is uncertain. As the pigments flow outwards the form of the chro- 

 matophore appears to change from an irregular to a " stellate," and then to a 

 " branched " one. The branches unite with those of neighbouring chromato- 

 phores, and so may form a network in which the " centres " are unrecog- 

 nisable. 



Blue Spots. — These spots, described on pp. 610, 611, may be surrounded by a 

 clear " halo " or transparent envelope crossed by " radiations," some of which 

 (red or blue) are usually thicker than the rest. 



Ant. The region of the body in front of the stomach. 



VOL. 43, PAKT 4. — NEW SERIES. Z Z 



