374 SYDNEY J. HIOKSON. 



On the opposite face of the mesenteries the muscular 

 processes of the endoderm-cells run transversely to the long 

 axis of the polyps. These may be seen quite clearly in any 

 good series of sections taken longitudinally through an expanded 

 polyp. They constitute what has been called the protractor 

 muscular system of the polyps (figs. 14 and 21^ P. msc). 



In the disc there is a circular band of muscle-fibres situated 

 in the ectoderm^ and from this baud there run fibres along 

 the borders of the inner surface of each tentacle. These fibres 

 undoubtedly act as the retractors of the tentacles (fig. 10). 



The Endoderra. — The method adopted for examining the 

 minute structure of the endoderm of Alcyonium was to place 

 some thin strips of a colony into \ per cent, osmic acid for 

 thirty minutes, then wash in distilled water and transfer to 

 picro-carmine for thirty minutes. The walls of the coelenteric 

 canals were then scraped with a fine scalpel, and the endoderm 

 thus removed teased up with needles in glycerine. A modifi- 

 cation of this method, which yielded some good results, was to 

 substitute a weak solution of gentian violet for the picro- 

 carmine. 



The cells lining the coelenteric canals are by these methods 

 seen to be very similar in their general characters to the myo- 

 epithelial cells (fig. 28). 



The protoplasmic portion contains a number of coarse 

 granules, which stain brown with osmic, and have strong 

 affinities for gentian violet. They are usually irregular in out- 

 line, but, owing to their very minute size, it is not possible to 

 assert that they have crystalline shapes. The granules are 

 probably of the same nature as the nutritive spheres which 

 occur in some of the endoderm-cells of the Hydrozoa. 



A few cells present one or more large clear vacuoles. 



The nucleus is round, and stains faintly in picro-carmine. 

 A careful and prolonged examination of these nuclei with the 

 highest powers at my disposal failed to reveal anything beyond 

 a clear homogeneous structure. I have never seen any stages 

 in the division of the nucleus. 



Most of the cells show a single very delicate flagellura on 



