Body Colour in Amphipods and Isopods. 159 
XI.—Body Colour as affected by Blood Colour in Amphipods and 
Isopods, with some Remarks on a Bacterial Infection of 
Gammarus. By John Tait, M.D., D.Sc. (From the Laboratory of 
Physiology, Edinburgh University.) 
(Read 26th February 1917. Received 26th February 1917.) 
THE observations here recorded have been made at intervals in the course 
of an investigation chiefly on blood coagulation in Crustacea (see Tait, 1, 2, 
5, and Tait and Gunn, 4). 
Bopy CoLourR AND Bioop CoLour. 
The discovery that Zigia oceanica undergoes a marked change in shade 
in response to its surroundings (Tait, 5) led me to pay attention to the 
colours of other forms. P. Mayer (6), Matzdorff (7), and V. Bauer. (8) had 
previously studied reflex colour change in Jdotea. Since the observations on 
Ingia were made, I have found that Spheroma serratuwm undergoes a similar 
change of shade in response to its background, whereas Oniscus and Conilera 
do not (Tait, 2). Piéron (9) in a recent paper, to which I have failed to get 
_ access, has also studied colour change in isopods. 
Chromatophores occur in the hypodermis of very many searrocls and 
naturally the colour of these animals is largely due to the chromatophores. 
On the other hand, the common shore amphipods (Gammarus marinus, 
G. locusta, Orchestia littorea, Talitrus locusta) have no chromatophores. Their 
colours are nevertheless very diverse. Among Gammari, which tend to be 
uniformly “self-coloured,” dark greens, slate-greys, and browns are common, 
dark reds are not uncommon, while pale yellows and whites are occasionally 
met with. Individual specimens of Orchestia or of Talitrus are more 
variegated, the ventral surface being lighter than the dorsal, probably in 
relation to their dorsi-ventral posture, while the dorsum tends to be 
transversely banded. Orchestia is either brown (or blue and brown) above 
and bluish below, or of a bright yellow-brown with no sign of blue below. 
Talitrus is much paler, only the dorsum being marked with pigment. ‘These 
colours, in contrast with those of some of the isopods mentioned above, are 
permanent (over considerable periods of time) in spite of change of surround- 
ings or of lighting. 
Examination shows that the colour of the blood of these amphipods 
closely corresponds with that of the animals themselves. A dark green 
Gammarus has greenish blood plasma, a slate-grey specimen bluish plasma, 
a brown has brown, while a brownish-red has violet plasma. The pale yellow 
and the white Gammari have plasma that is almost colourless, while the 
