308 PROCEEDINGS OF THE ACADEMY OF [May, 



It is said that the lining of the ' ' mid-gut ' ' comes out when the 

 posterior half of the test is shed (Schonichen), and this I have seen 

 in a number of cases. Sometimes, however, the lining is not to be 

 found with the posterior half, but remains in the lumen attached, 

 it may be, at some point. The habit of eating the posterior test 

 (see note 7) may possibly be concerned with detaching the lining 

 in such cases. The lining begins to break loose from the epithelial 

 cells before there is any apparent sign of tlie external moult. Fig. 

 8, from an animal in the act of casting its intestinal liniug, pre- 

 sents an appearance in striking contrast with that seen in other 

 physiological conditions. Tlie fibres are wholly wanting on the 

 luminal side of the nucleus, and the cytoplasm has a uniformly 

 granular aspect ; the alveolar structui-e is almost entirely masked by 

 the granules, so that only rarely does one get a glimpse of it even with 

 high powers. The palisade at the luminal edge is not to be seen. 

 Schonichen has observed this disappearance and concludes that the 

 chitinized ends of the fibres (Balkchen) function in breaking loose 

 the intima, in the way the " little hairs " described by Braun (22) 

 are said to do for Astaeus. He has not, however, noticed the differ- 

 ence between the two cases, namely : that in Astaeus the little haii-s 

 are to be seen in the test both during the shedding and after it has 

 taken place, whereas in the isopods the fibres wholly disappear. 

 The disappearance of the fibres is too complete to be accounted for 

 by the mere masking of the alveolar structure by means of gran- 

 ules. This is in strong contrast with a case of masking which 

 occurs when the end of the cell is filled with small granules, refer- 

 able to the process of food absorption (fig. 11, J5). The thick- 

 ened portion of the fibres does not disappear in such masking; 

 they may even appear more sharply defined than where such 

 granules are not present (fig. 11, J.). At a later stage in the 

 process of moulting, fibres, very much finer than those which still 

 exist unaffected by the moult in the coelomic side, can be traced 

 in the luminal side after the new intima has attained some thick- 

 ness. The fine fibres do not possess the strong afiinity for stains 

 which they have later. From the foregoing facts it is only reason- 

 able to suppose that the fibres in the luminal side of the cell con- 

 tribute to the formation of the substance by whose transformation 

 the new intima is formed ; and that their disappearance at the time 

 of moulting is due to some process of dissolution, the fluid thus 



