Development and Mode of Growth of Diplogeaptus. 239 



shows two oval wrinkled chitinous plates, the gonangia, and 

 between them two bundles of radiating siculse, which are prob- 

 ably part of the contents of two other gonangia. The appear- 

 ance of these bundles and of others similar to that represented 

 in fig. 16, suggests the idea that the basal siculse were not 

 detached, and perhaps, by shrinkage of the blastostyle, gained 

 connection with the central disc and funicle. The existence of 

 bundles of hydrocauli (cf. PI. II, ^g. 3) springing from the base 

 of grown colonies, is in favor of this view. The dense bundles 

 of siculae on young colonies indicate that most, if not all, of the 

 sicula3 remained in connection with the parent colony, while the 

 appearance of the older colonies leaves no doubt that multitudes 

 of siculae became detached. 



These bundles of siculae now begin to develop, at first, by 

 extending the hydrocauli (fig. 17), after which the production 

 of hydro thecae sets in (fig. 18). It may be concluded from figs. 

 IT and 18 that the young rhabdosomes did not all develop alike. 

 While in fig. 17 most siculae do not yet bear a theca, others have 

 already one and a few have still more, even as many as five 

 thecae. In the specimen represented in fig. 18 the majority of 

 the siculae has produced one theca, and in the original of fig. 19 

 most of the rhabdosomes bear about half a dozen thecae. In. 

 this excellently preserved specimen the hydrocauli no doubt take 

 their origin from the central disc and the inclosed funicle ; 

 funicle, central disc and cyst are here preserved with their chitin- 

 ous tests. The upper rhabdosome is so far advanced that it 

 probably is the primary one. There is no primary rhabdosome 

 preserved on the original of figs. 17 and 18. In such specimens 

 as are represented in figs. 20 and 21 is a more advanced stage. 

 On the former specimen may be observed, besides the young 

 rhabdosome, a complete chitinous gonangium (g), a dense multi- 

 tude of radiating siculae at the right and some single siculae at 

 the lower side. Because of the great difference in age between 

 the siculae and the young rhabdosomes I am inclined to regard 

 the gonangia and siculae as a second generation, produced after 

 the first generation had reached a certain age. The basal cyst is 

 preserved in this specimen as in many others as a strong plate 

 with a chitinous border, apparently the result of the filling of the 

 empty bladder with sediment. 



