ALCYONIHVE. 263 



zooids therefore have become incapable of capturing and digesting food. The increased 

 circulation brought about by their specialisation would relieve the autozooids to a 

 certain extent of that function, hence the feebly marked siphonoglyph in the autozooids 

 of Sarcophytum and Lobophytum. 



The stomodaeal ectoderm of the siphonozooids in Sarcophytum and Lobophytum is 

 composed of the same elements as in the autozooids, but owing to the physiological 

 division of labour they occur in very different proportions. 



In the stomodseum of the siphonozooid there is a pronounced increase in the 

 number of flagellate cells, so that the siphonoglyph is proportionately larger than in 

 the autozooid this is accompanied by a very pronounced reduction in the number of 

 granular gland cells, which are extremely rare in these two genera, but are entirely 

 absent in Scleropkylum. The stomodfeum of the siphonozooid in Sarcnphyfam and 

 LobopJiytum consists chiefly of flagellate cells, which constitute the well marked 

 siphonoglyph and the ciliated columnar epithelial cells which line the remaining 

 portion of the stomodfeum. Among the latter are interspersed a few interstitial cells, 

 nematocysts, scleroblasts, and a very few gland cells. 



Siphonozooids and autozooids frequently communicate with each other by means of 

 short ciliated canals, which differ from the vessels of the canal system in the presence 

 of long columnar endoderm cells provided with fairly long cilia (fig. 22). 



In Scleropliytum modification of the stomodfeal ectoderm has proceeded still 

 further. In this genus the siphonozooids are very much reduced. The stomodeeum 

 has neither flagellate cells nor gland cells, but consists in the species S. dcnsum and 

 S. hirtum (fig. 20) of a short simple tube opening to the exterior and lined apparently 

 by undifferentiated ectoderm cells. In the species S. palmatum and S. capitals there is 

 no aperture to the exterior ; in S. durum and S. polydactyhnn, an aggregation of a very 

 few ectoderm cells is the degenerate representative of the stomodceum in other forms. 

 The stomodfiBum is entirely unrepresented in S. gardincn and >V. querciforme. 

 Mesenteries are only present in very few cases and are extremely small and very 

 feebly developed (fig. 20 m). 



DEVELOPMENT BY BUDDING. 



The siphonozooid buds differ from those which are destined to become autozooids 

 in that their development is arrested at a very early stage, which appears to be 

 constant for the species, and also to a certain extent in development, although the 

 very early stages of both forms of zooids are identical. 



In Sderophytum the siphonozooids are extremely small and retain throughout life 

 their intimate connection with the transverse vessels of the canal system from which 

 they originated. In the development of the siphonozooids of S. dcnsum a c;ecum is 

 formed by an outgrowth from an endodermal canal near the surface of the colony. This 

 is accompanied by a multiplication and aggregation of the ectoderm cells at the surface, 

 immediately opposite the caecum (fig. 20). These cells arrange themselves so as to 



