Intracellular canals in the skin of Phascolosoma. 195 



of the reticulum of the cell — that the outer wall of the vesicle, the 

 wall of the ampulla and the wall of the tube, are formations of the 

 cytoplasm analogous to cell and nuclear membranes. 



Manille Ide (1891) published extensive comparative studies upon 

 the intracellular canals found in the cutaneous glands of various 

 Crustaceans, together with a careful review of the literature upon the 

 subject of intracellular canals. He concludes that gland cells with 

 intracellular canals are to be traced back to the simple type of uni- 

 cellular glands. He conceives that in case of certain secreting cells, 

 one end of the cell becomes a neck by reason of mechanical pressure 

 — that such a neck may take on a chitinous wall and come to serve 

 a purely conducting purpose — that differentiation may go still 

 farther until the product of secretion localizes itself and takes on a 

 wall similar to that of the conducting canal, of which it is simply a 

 prolongation. Other differentiations may follow in the cytoplasm, for 

 example, a radial vesicle and sheath such as Gilson describes for 

 Bla2)s. 



In a recent paper Zimmermann (1898) describes for the Crustacean 

 Phronima some peculiar three-celled glands, containing a complicated 

 system of intracellular canals. The duct resulting from the union of 

 this system of canals traverses a long thread-like cell in which the 

 nucleus lies closely applied to the duct. This elongated cell is prob- 

 ably comparable to the cell forming the sheath for the main duct 

 in Phascolosoma. 



Concerning the origin of these intracellular canals, there may be 

 offered the two hypotheses already suggested by Bolsius (1890), for 

 the intracellular canals in the nephridia of leeches: 1) that the 

 intracellular cavity is formed within by a special differentiation of the 

 cytoplasm, and is secondarily brought into communication with the 

 exterior ; or, 2) that an invagination of the membrane of the cell has 

 taken place. For the solution of the question, embryological material 

 must be studied, and this I have unfortunately been unable to obtain. 



University of Minnesota, 

 April, 1899. 



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