THE ALCYONARIA OF THE MALDIVES. 519 



brazilin, but the superficial canal system is best observed in stained microtome sections about 

 20 /i in thickness. These sections however are too thick for histological purposes. The trans- 

 verse superficial canal system is extremely well-marked in most species. The principal vessels 

 are comparatively broad channels, which run also immediately below but parallel with the 

 surface (fig. 22 t. s. c.) ; these I have named the " transverse canals." The vessels of this 

 system ramify and anastomose throughout the peripheral tissues, they communicate with the 

 terminal portions of vessels of the internal system, and have numerous apertures into the 

 coelenteric cavities of neighbouring autozooids (fig. 22 ap. c). From these vessels buds arise 

 towards the surface, which in Sc. gardineri and Sc. querciforme develop into autozooids. In 

 all the other species in the collection buds are extremely numerous and are very regularly 

 arranged near the capitular surface, and differ from autozooid buds (1) in that they are all 

 arrested at a very early stage, which appears to be constant for the species, and (2) differ 

 also to a certain extent in development. There can be no doubt that these buds are 

 homologous to the siphonozooids of Sarcophytinn and Lobophytum, from which they differ in 

 that their growth and development are arrested at a much earlier stage. These rudimentary 

 siphonozooids retain throughout life their intimate connection posteriorly with the transverse 

 vessels from which they originated (fig. 22). In Sc. capitale, Sc. densum, Sc. palmatum, and 

 Sc. hirtiim development is not arrested until the rudiments of a stomodaeum with mouth 

 aperture and rudiments of mesenteries have been formed. In Sc. durum and Sc. polydactylum 

 development is arrested at an earlier stage, a few ectoderm cells representing the stomodaeum 

 wander into the mesogloea about the terminal portion of a bud, but there is no mouth 

 aperture, and the bud is simply a caecum from a transverse canal, with only traces of 

 mesenteries. In dimoi-phic species the number of siphonozooids arising from a transverse canal 

 varies, but in Sc. capitale seven or eight siphonozooids terminating in a single vessel may 

 often be counted between two autozooids. 



In the presence of a special superficial canal system this genus is completely separated 

 from Lobophytum, Sarcophytum, and Alcyonium, but in this respect it approaches Xenia. 

 Zoochlorellae are numerous in the endoderm of the superficial canals, and are present in 

 varjdng numbers in the lumen of the canals. 



The internal canal system is strongly marked and is very similar to that of Xenia. It 

 differs from that of Sarcophytum and Lobophytum in that the siphonozooids do not terminate 

 posteriorly in the longitudinal vessels of the system, but in the transverse vessels (fig. 19). 

 The principal vessels run more or less parallel mth the longitudinal direction of the auto- 

 zooids and have numerous apertures into their coelenteric cavities (fig. 22 ap. c). They 

 ramify and anastomose throughout the internal and especially in the basal portions of the 

 colony. Many vessels terminate near the periphery in the vessels of the superficial canal 

 system. Zoochlorellae are only to be found in this system in those canals which lie near 

 the surface. 



Zoochlorellae are present in all the specimens of the genus in the collection, but they 

 vary in number in different species. Theii- numbers, however, do not appear to be affected 

 by bathymetric variations within certain limits, for they are fairly numerous in specimens 

 which have been taken at a depth of from 24 — 34 fathoms (Table I. p. 531). They are 

 most plentiful in Sc. gardinen and least in Sc. capitale, both of which species were taken 

 only in shallow water. 



I have suggested (p. 528) that their presence in enormous numbers in Sc. gardineri is 



