CALCAREOUS SKELETON OF THE ANTHOZOA. 507 



illustrating the formatiou of the spicules in the lower moieties 

 of the exserted portions of the polyps. 



The scleroblasts of Alcyoniura digitatum (PI. 40, fig. 1) 

 have the form of irregularly polygonal, ovate, or araoebiform 

 cells, varying very much in size and shape, but resembling 

 one another in the coarsely reticulated structure of the proto- 

 plasm, and in their dark granular appearance. Vacuoles of 

 small size (not the ultimate vacuoles of Biitschli) are visible 

 in the protoplasm, and not infrequently a vacuole contains a 

 single microsome. The scleroblasts run in strands and 

 patches through the mesogloea at the bases of the expanded 

 polyps, and may be found, though they are not easily studied, 

 in the thickened raesoglcea of the coeuenchyme. They are 

 always accompanied by two other kinds of cells whose function 

 is obscure. The one kind, marked gr. in fig. 1, are rather 

 smaller than, but of similar shape to, the scleroblasts, and are 

 filled with minute highly refringent granules; their nucleus 

 is rarely to be seen, being hidden by the granules. My studies 

 on other Alcyonaria lead me to believe that their function is 

 to secrete the gelatinoid substance of the mesoglcea. The 

 second kind of bodies I call provisionally the ovoid bodies. 

 Each of these is about -0075 mm. in length, is surrounded by 

 a protoplasmic sheath, and has a relatively large nucleus on one 

 side of it (fig. 1, ou.). These were noticed but not well figured 

 by Hickson (13), and similar structures were observed by von 

 Heidcr in Cladocora. Hickson suggests that they may 

 possibly be parasitic sporozoa, but my observations do not lend 

 any support to his suggestion. Their contents are clear and 

 highly refringent, but are not calcareous. They are not 

 affected by prolonged treatment with dilute acids; they are 

 unaffected by treatment with acetate of potash (used with the 

 view of precipitating lime if any was held in solution) ; they 

 do not light up when viewed through the polariscope with 

 crossed Nicols. They stain deeply with hsematoxylin, but are 

 unaffected by other dyes. I have met with similar ovoid 

 bodies among the scleroblastic cells of all the Anthozoa which 

 I have examined carefully, and I am unable to guess their 



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