REPORT ON THE PENNATULIDA. 149 



transverse section varies in shape according to the size of the spicules. 

 The smaller spicules are, as shown in Fig. 6, very distinctly triradiate, 

 but of a heavier and less elegant pattern than in FtinicuUna (c /, Plate 

 I., Fig. 9). In the larger spicules the grooves between the ribs are 

 filled up more or less completely, as shown in Fig. 7, while the largest 

 spicules of all have entirely lost the triradiate character, and are 

 circular in section. This relation between the size of the spicules and 

 their shape in tranverse section appears to be a very constant one, so 

 that for each length of spicule there is a characteristic shape in 

 section, which is rarely departed from to any considerable extent. 



The spicules are not uufrequently rather wider in the middle than 

 towards the ends, which latter are slightl.v rounded off. As already 

 stated, the spicules are bright red, the red colour of the leaves and 

 rachis being due entirely to them. 



c. The Tentadea, as in FunicuUna, are eight hollow processes of the 

 body-wall placed round the mouth, and bearing on each side a row of 

 from ten to fifteen hollow pinnules (Fig. 6../'). The tentacles are shown 

 in transverse section near to their bases in the uppermost section of 

 Fig. 5, which shows their structure at this part. Each consists of an 

 outer .la3'er or ectoderm, with abundant thread-cells or nematocysts ; 

 an endoderm lining the central canal, and continuous with the 

 endoderm of the body-cavity ; and a mesoderm, which at the sides and 

 inner surface of the tentacle is thin, as in FunicuUna, and consists 

 principally of a layer of longitudinal muscles, with an inner much 

 weaker laj-er of circular muscle-fibres. At the outer side of the 

 tentacle the mesoderm (Fig. .5) is very much thicker, and resembles in 

 structure the mesoderm of the body-wall, consisting, in addition to an 

 outer layer of longitudinal muscles, of a gelatinous connective-tissue 

 matrix in which are embedded a number of calcareous spicules 

 (Fig. 5, i). 



The pinnules are at the lower end of the tentacle rather long, 

 thin, and some distance apart ; towards the upper end they become 

 thicker and more closely set together. Their cavities open into the 

 central cavity of the tentacle, and their structure is the same as that 

 of the tentacle itself. They may even contain small calcareous 

 spicules. 



d. The StomacJi, as seen in Figs. 4 and 5, is very similar to that of 

 FunicuUiM. It is short, and is entirely contained in the free portion of 

 the polype. Its walls are thrown into transverse folds, which, when 

 the polype is retracted, are approximated like the folds of a concertina 

 so as to reduce the stomach to less than half its normal length. 



The walls of the stomach agree in structure with those of FunicuUna, 

 consisting of a thin glandular linmg membrane or ectoderm, which is 

 distinctly ciliated, a thin connective-tissue mesodermal layer, and a 

 moderately thick outer or endodermal layer, containing numerous 

 spherical highly refractive granules similar to those described in 

 FunicuUna. 



