PORIFERA, CCELENTERATA, VERTEBRATA 73 



Demospongise, and few observations have been 

 made upon their archeocytes. These archeocytes 

 are of the greatest importance since they give rise 

 to the amebocytes and tokocytes (reproductive cells) . 

 According to Weltner (1907) both amebocytes and 

 tokocytes are only physiological states of one and 

 the same kind of cell. Many authors have em- 

 phasized the importance of the amebocytes, such as 

 Gorich (1904), who maintains that this class of cells 

 gives rise not only to the gonocytes, statocytes, 

 and trophocytes, but also to certain pinacocytes. 

 Weltner (1907) goes further than this when he states 

 from studies upon the fresh-water sponge that the 

 sponge could not exist without amebocytes. 



The earlier investigators almost invariably con- 

 sidered the germ cells as mesodermal in origin. 

 Lieberklihn (1856) discovered the eggs in Spongilla 

 and later (1859) in Sycandra raphanus. Sponge 

 eggs were also observed by Kolliker (1864). Haeckel 

 (1872) thought that the eggs were derived from the 

 flagellated cells of the gastral epithelium. Schulze 

 (1875), on the contrary, maintains that they lie 

 deep in the so-called mesoderm ; and Fiedler (1888) 

 concludes that in Spongilla only certain cells of the 

 middle layer may become germ cells. 



Maas (1893) distinguished two sorts of cells in the 

 middle layer; one characterized by uniform, fine- 

 granuled cytoplasm and an oval nucleus containing 

 a very fine net- work of chromatin; the other filled 

 with coarse-granuled cytoplasm and a spherical nu- 

 cleus containing a deeply staining nucleolus and 



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