342 PROCEEDINGS OF THE ACADEMY OF [May, 



The constituent which gives chai-acter to the cells under considera- 

 tion is the zymogen (figs. 20-23). In the fresh condition it is 

 always seen as a dense mass of spherical yellowish granules sur- 

 ?-ounding the nuclei of the smaller cells. They are but rarely seen 

 in the tall cells, the most obvious constituent of these being, as we 

 have observed above, the oily-looking globules. On this account 

 Weber called the smaller the " ferment cells," as opposed to the 

 larger or "liver cells." Rosenstadt (44) for Asellus, Giard and 

 Bonnier (45) for the parasitic Isopods and Frenzel (46) for the 

 marine forms, as well as for Oniscus murarnts, do not admit this 

 distinction made by Weber. Claus says they are only extremes 

 of the same kinds of cells, in no way to be distinguished. Frenzel 

 regards the smaller as young cells and the larger merely as a later 

 or older phase. He concludes, therefore, that the isopods are to be 

 classed with the Phronimidse, in that they produce both ferment and 

 fat in the same cell, as over against the decapods, the Gammarida9 

 and Caprellidse, which produced these in separate cells. Ide is in- 

 clined to adopt the view of Weber. My results confirm Frenzel, 

 as will appear in the following discussion. 



The behavior of the zymogen granules with reference to reagents 

 is as follows. As was observed by Huet, they are speedily dissolved 

 out by both water and alcohol. Reference to Table I, v/here are 

 brought together data from a long series of different physiological 

 conditions, shows that they are not preserved by alcohol (Nos. 24, 

 36, 38), only partially by picro-acetic (29, 43), and sometimes not 

 by sublimate (28, 31), nor by sublimate-acetic (3, 9, 11, 13, 22, 

 41, 42, 44), nor formo-alcohol (32). They are always preserved 

 by Flemming's, Hermann's and Hermann's without aectic (also 

 osmic-acetic and osmium-bichromate, Altmann's). It will be seen 

 also from the table that they are sometimes preserved in the small 

 cells and not in the large ones (Nos. 11, 13, etc.), sometimes 

 again in both kinds of cells, where they appear precisely alike (Nos. 

 15, 18, 26, etc.). With the osmic fixations, particularly the 

 platinic-chloride-osmic acid mixture, they behave a little differently 

 in the two kinds of cells. The densely aggregated granules about 

 the nuclei of the small cells come through the stains wholly un- 

 seen extending opposite to the direction of penetration, while they are 

 also occasionally seen in tiie cells of the hepatopancreas, extending to- 

 ward the lumen after fixation ; thirdly, as was remarked in the begin- 

 ning, nuclei in the fresh condition are regularly curvilinear. 



