62 GC. A. MAC MUNN. 
that the ovaries evidently contained two lipochromes ; a xan- 
thophan- and rhodophan-like one. 
The digestive gland had a brownish colour, and ex- 
tracted with alcohol yielded an orange-yellow solution, a 
deep layer of which transmitted red and some green, while a 
shallower one gave one band in the green from about 2 526 to 
A 468 (including the feebly-shaded part); this is evidently the 
same band as that seen in the blood. On evaporation a red, 
and in parts an orange, residue was left, soluble in ether with 
a yellow colour, and the latter solution had the same absorptive 
property as the alcohol solution. It was also soluble in chloro- 
form with an orange colour, absorbing all but the red and a 
little of the green in a deep layer, and in less deep giving one 
broad band extending in its darkest part from about A 503 to 
\ 474, On touching this residue with a drop of nitric acid it 
became blue and greenish, with sulphuric acid a dirty green, 
brown, and violet, with iodine in potassic-iodide perhaps green. 
No enterochlorophyll could be detected. I have no doubt 
that, as appears to be the case in crustacean blood, the red, 
rhodophan-like lipochrome is built up in the digestive gland 
and carried in the blood current to be deposited in other parts 
of the body, though what its rdle may be when deposited there 
it is difficult to say. It is not easy to see of what use so much 
brilliant colouration as exists within the body of Holothuria 
nigra can be, except that the lipochrome is changed into some 
other constituent. If,indeed, it be respiratory, as tetronerythrin 
is believed by Merejkowsky to be, we could see some reason 
for its existence, but, as I have repeatedly shown, what has been 
called tetronerythrin does not exist in two states of oxidation. 
Merejkowsky would doubtless call the red lipochrome of H. 
nigra tetronerythrin without hesitation; but since he pub- 
lished his results our knowledge of these fat pigments has 
undergone a change, for we now know that there are a great 
number of pigments, formerly with regard to their supposed 
respiratory properties, included under the name tetronerythrin, 
which are distinguishable from each other, and which cannot 
any longer be called tetronerythrin, the rhodophan of the retina 
