1902.] NATURAL SCIENCES OF PHILADELPHIA. 307 



regai'ds the chromatin as a more or less complete solution of nuclein 

 bodies, which are precipitated ordinarily in the form of granules by- 

 fixing fluids. If the chromatin is already in the form of alveoles, 

 over-fixation might result from too rapid action of the fluid on the 

 periphery of the alveole, preventing a deeper penetration, and con- 

 sequently preventing complete precipitation in the form of a granule. 

 The " skein-like " arrangement (pelotonee) of the chromatin of v. 

 Bambeke would thus be accounted for. Certainly the " osmi- 

 cated " nuclei look as if such a partial precipitation had taken 

 place. How to regard the strands which appear in distorted 

 nuclei (Fig. 7, A), whether as the mere elongation of alveoles or 

 as due to I'upture with escape of chromatin contents, I am wholly 

 undecided. I hope to make this and related subjects the object of a 

 special study. 



(4) Moulting. 



"We have now considered the normal cellidar structure common 

 to all physiological conditions, except those incident to the shedding 

 and renewal of the lining. Early in the course of this study it 

 became necessary to separate clearly the changes occurring in the 

 cell during these processes from those connected with the phe- 

 nomena of absorption of foods. It is well known that the land 

 isopods moult frequently during the spring and summer. Kept in 

 the Vivarium and Laboratory at temperatures corresponding to 

 these seasons, the moults take place in a perfectly normal manner 

 even in winter, and may easily be observed. It is well known, too, 

 that the test of the isopod is cast in two pieces. The posterior 

 piece, which comes off first, reaches to the anterior border of the 

 fifth thoracic segment. One or two days may intervene before the 

 anterior piece is shed,' 



' In two cases observed in February, of which I kept careful account, 

 the time was about forty-eight hours from the complete detachment and 

 removal of the posterior half until the animal was freed from the anterior 

 half; in several other cases observed in July the time was twenty-four 

 hours. A number of animals kept in dishes were suspected of eatiug the 

 posterior test while the mouth-parts were still hard. Quite recently I 

 liave obtained indubitable evidence that this occurs in the natural state. 

 In a number of animals found with the anterior half still soft the mtea- 

 tine was filled with a chalky-looking substance, which proved on exami- 

 nation to be finely broken bits of the chitiuous skeleton ; no entire poste- 

 rior test was found with these animals. The purpose of this habit is 

 probably to utilize the calcareous matter. 



