and Decapod Crustacea : its Structure and Functions. 



formol. After from 12 to 24 hours the preparation is transferred to 

 alcohol of 95 per cent., and, when hard enough, to a mixture of alcohol 

 and ether, and finally into a solution of celloidin. When this is set, 

 the preparation is cut either in the ordinary way, or by the freezing 

 microtome. Clearing is done by means of oil of sandalwood, or oil of 

 origanum. The sections were stained in various ways, but the best 

 results are obtained with hsemalum, followed by eosin as a plasma 

 stain. I also used mucicarmine, thionin, "Soudan III," and other 

 stains for special purposes. In this way very satisfactory preparations 

 can be obtained, and the celloidin keeps all the gland constituents 

 in situ. 



The glandular epithelium in the Crustacea contains, according to 

 Max Weber, two kinds of cells, hepatic cells and ferment cells. 

 Frenzel subsequently called them fat-cells, or fat-holding cells, and 

 ferment-cells. That of mollusca contains, according to Barfurth, 

 hepatic cells, and ferment cells also, which Frenzel again re-named 

 granular cells and club-cells. Now the sharp distinction drawn between 

 these kinds of cells by these observers is found not really to exist, and 

 we meet with transition-forms between them. The coloured contents 

 of these cells, in the case of either ferment-cells or granular-cells, or 

 fat-cells, are coloured by either enterochlorophyll or by a lipochrome, 

 or by both. 



It was, however, mainly my object, after having studied the histology 

 of the gastric gland, to find out if I was really justified in calling this 

 colouring matter enterochlorophyll, and if it has properties which class 

 it among the chlorophylls, to find out how it gets into the gland, and 

 so on. 



It is impossible here to refer more fully to the histology of the 

 gland, so that I shall merely give an account of the observations on 

 the pigments found in it. 



The only way in which any pigment giving a banded absorption- 

 spectrum can be readily identified is, of course, by means of the spectro- 

 scope, but since spectrum analysis alone is attended by certain fallacies, 

 one has to fall back on spectrophotometry. This being a quantitative 

 method gives the most accurate results of all. Of course elementary 

 analysis, if applicable, enables one at once to decide the identity or 

 non-identity of pigments, but unfortunately the pigments with which 

 we are now dealing cannot be prepared in a pure, or even in an approxi- 

 mately pure, condition for this purpose with our present knowledge, 

 owing to their being mixed with fatty matters and other impurities. 



The spectrophotometer which I have used is a modified form of that 

 which Yierordt introduced. Some of the modifications were, I believe, 

 introduced by the brothers Kriiss ;* others were suggested by me to 

 Mr. Hilger, who constructed the apparatus. 



* G-. and H. Kriiss, ' Kolorimetrie und Quantitative Spektralanaljse.' 1391. 



2 L 2 



