298 J. H. ASHWOETH. 



3. The non- retractile nature of the bodies of the polyps 

 and of the stems is accounted for by the absence of muscle- 

 fibres from their ectoderm cells^ and by the presence of 

 numerous spicules in these parts. The presence of ectodermic 

 muscles in the tentacles, pinnules, and distal millimetre of the 

 bodies of the polyps, together with the absence of spicules 

 from these parts, confers the power of contractility, slight 

 though it is, upon these parts. The muscle processes of the 

 ectoderm cells (where present) are longitudinal in direction, 

 while those of the endoderm cells are circular (except the pro- 

 tractor and retractor muscles on the mesenteries). 



4. Nematocysts were found in Sarcophyton. 



5. An extraordinary number of spicules is present in the 

 basal part of the colony, and much of the mesogloea is converted 

 into a dense horny substance. Thus a firm base of attach- 

 ment is provided which would afford a rigid support for the 

 branches which arise from it. 



6. Many of the endoderm cells lining the coelentera and 

 tentacles bear giant flagella, which may attain 120 ju in 

 length. 



7. In adult polyps the primitive genital cells are formed by 

 differentiation of some of the endoderm cells which cover the 

 mesenteries. These genital cells migrate into the mesoglcea 

 of the mesenteries, and then move outwards, one at a time, 

 each cell pushing the endoderm and a thin film of mesogloea 

 before it, and so forming a small tubercle on the side or 

 end of the mesentery. By division of the genital cell the 

 spermatozoa are produced. They remain until ripe, surrounded 

 by a thin film of mesogloea, and by a layer of endoderm cells, 

 many of which contain from two to five nuclei. 



8. The longitudinal canals which traverse the mesogloea 

 of the stem are very well developed, and are physiologically, 

 and possibly morphologically, equivalent to the coenenchymal 

 tubes of Heliopora ccerulea. 



9. The nervous system is similar to that of Alcyonium; 

 the stellate cells immediately outside the endodermic muscle- 

 fibres are very clearly seen. 



