302 J. H. ASHWOETH. 



of the ventral mesentery (F. M.), and the connection of the ceelenteron with 

 the canal system are shown. Three ccelentera of older polyps are also shown. 

 Two of them are crowded with sperm sacs {S. S.), many of which, owing to 

 mutual pressure, have lost their original spherical shape and are pentagonal 

 or hexagonal in section. The otlier ceelenteron contained a similar number of 

 sperm sacs, but they have been omitted in order to more clearly show the 

 dorsal mesenterial filament {D. 31. F.) and the thin edge of the ventral mesen- 

 tery {V. M.). The superficial {Sup. Can.) and longitudinal {Lo7ig. Can.) canal 

 systems, and their relation to each other and to the ccelentera; the denser 

 cylinder of mesoglcea {Mg. D.) with its surrounding ectoderm cells enclosing 

 each ceelenteron ; and the distribution of spicules, uematocysts, and zooxan- 

 thellai are also shown, x 35. 



Fig. 9. — A thinner transverse section through the upper part of one of 

 the stems. Tiie ccelentera in the peripheral part are smaller than those 

 nearer the centre. The ceelenteron of a very young polyp is seen on the 

 right. The cells in the mesoglcea of the mesenteries and sperm sacs in 

 various stages of development, attached to the mesenteries of the older ccelen- 

 tera, are also shown. The number of flagella cut across in one section is seen ; 

 thus an idea may be formed of their abundance and of their size relative to 

 the eudoderm and to the ccelentera. Many of the features to which attention 

 was drawn in the description of the previous figure are also shown here. 

 X 50. 



Fig. 10. — Transverse section through a polyp at the level of the lower 

 third of the stomodseum. The chief features shown are the gland-cells and 

 siphonoglyph of the stomodseum, the somewhat feebly developed retractor 

 muscles on the mesenteries, and the distribution of the spicules, nematocysts, 

 and zooxanthellse. X 50. 



Fig. 11. — Transverse section of the outer wall of a pinnule showing the 

 ectoderm containing nematocysts, the mesoglcea, and the endoderm cells with 

 their reticulate protoplasm. X 800. 



Fig. 12. — A nematocyst in its cnidoblast cell, from a sectioa. One half of 

 each coil of the thread in the upper part of the nematocyst was cut away in 

 sectioning. X 2000. 



Fig. 13. — Eight large spicules selected from those in the base of the 

 colony. Each spicule is situated in a small cavity in the mesoglcea. The 

 nucleus and remains of the protoplasm of the spicule-forming cell arc seen. 

 From sections. X 800. 



Fig. 14. — A portion of the outer part of the mesoglcea from a transverse 

 section of a polyp. Four of the spicules present their edge and two their 

 flat face to the observer, x 800. 



Fig. 15. — Two very young spicules in their respective cells. The spicule 

 in Ah'i^ {i long and 2^ ju broad. The spicule in B presents its edge to the 

 observer. It is 7 m lo"g ^^^ 1^ h thick, x 1000. 



