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stained in haematoxylin, I have repeatedly seen, in the largest lacunae, 

 a small spherical body stained dark blue. It has every appearance 

 of being a nucleus, and I see no reason, aside from its singular 

 position, to doubt that it is one. In the smaller lacunae one rarely 

 sees any evidence of protoplasm or of a nucleus. All these facts 

 show, beyond any possible doubt, that we have to deal here with 

 actual cavities and canals in the chiten, of definite shape, and filled 

 with nucleated protoplasm. 



The lacunae arise as enlargements of the distal 

 ends of the canaliculi. One can observe various stages of the 

 process in the same individual or even in the same section, fig. 3. 

 In this case the section passes through the point of union of three 

 trabeculae. At such points in old crabs, the lacunae are very 



Fig. 3. 



a.o. 



numerous and apparently vary a good deal in shape, due to the 

 fact that the lacunae are here turned in various directions so that 

 some are cut crosswise, others lengthwise. The lacunae are filled 

 with air and appear black. The canaliculi, as they enter the darker 

 axial core, a— b, are sinuous, and very minute branches are given off 

 from them which terminate in minute lacunae. The latter increase 

 in size, and, as shown by intermediate stages, appear to move away 

 from the main canal and finally to communicate directly with the 



