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SUMMARY OF CURRENT RESEARCHES RELATING TO 
combination between a red lipocbrome and an organic base, probably 
derived from tlie muscle. The red colour of the shell in Nephrojps is 
due to the same red lipochrome in combination with lime. The green 
colour of the eggs of the lobster the author finds to be due to the 
mingling of the blue pigment of the shell with a yellow pigment, which 
also occurs in the liver and shell, and which does not give the lipochrome 
reactions. There is some evidence to show that this yellow pigment is 
capable of being transformed into the red lipochrome. The author 
is of opinion that the yellow pigment of the liver (hepatochrome) is 
widely distributed among the Decapod Crustacea, that it may be 
modified into the red lipochrome which may directly colour the shell, 
or may become converted into the blue compound. The numerous 
colour variations of the group are thus in part accounted for. 
Photomechanical Changes in Retinal Pigment-Cells of Palsemc- 
netes.* — Dr. G. H. Parker gives the following general summary of his 
results. (1) The only parts of the retina in Palsemonetes that exhibit 
photomechanical changes are the three kinds of pigment-cells. (2) The 
proximal retinular cells contain black pigment-granules. In the light 
these are diffused with slight concentration at the distal end and around 
the rhabdome ; in the darlc the jugment is limited to the retinal nerve- 
fibres. (3) The change from the dark to the light condition takes 
30-4.5 minutes ; the reverse change 45-60 minutes. (4) The changes 
are probably due to the internal protoplasmic movements. 
(5) The accessory pigment-cells have a yellowish-white pigment ; 
in the light this is massed partly at the base of the retina, partly near 
the distal surface of the first optic ganglion ; in the darlc it is almost 
wholly at the base of the retina. (6) The change from dark to light 
condition takes 45-60 minutes; the reverse change 105-120 minutes. 
(7) The changes are probably due to amoeboid movements of the cells. 
(8) The distal retinular cells contain black pigment granules. In 
the light they are contracted, and occupy a proximal position in the 
retina surrounding the axis of the ommatidium near the outer ends of 
the proximal retinular cells ; in the darlc they are expanded (flattened), 
and occupy a distal position in the retina, surrounding more or less 
completely the sides of the cone. (9) The change from dark to light 
condition takes 90-105 minutes ; the reverse change 105-120 minutes. 
(10) These changes are produced in part by an amoeboid movement of 
the cell, and probably in part by a muscle-like contraction of its axial 
portion. 
(11) Each set of photomechanical changes in the light is more 
rapid than the reverse set in the dark. (12) The conditions of the two 
eyes are quite independent. (13) The photomechanical action within 
the retina is localised, small groups of pigment-cells responding to 
local stimulation. (14) The changes may occur even if optic nerve is 
cut. (15) They may occur almost completely even on excised retinas, 
(16) Incompleteness in such cases is probably due to the death of the 
retinal tissue. (17) The three kinds of retinal pigment-cells probably 
respond to direct stimulation from without, and are not influenced by 
nervous impulses from within. There is no good evidence in favour of 
normal double conduction of nervous impulses. 
* Bull. Mus. Harvard, xxx. (1897) pp. 275-300 (1 pi.). 
