4 Lightbown, Filaments in the Siphonozooids of Pennatulacea 



Occurence of Filaments in Genera Examined. 



Where the number of species under consideration is limited and 

 incompletely representative it is impossible to make any absolute 

 generalisations : furthermore, subsequent re-classification may 

 destroy their value to some extent. It will be noted that the sub- 

 mergence of two of Kolliker's genera creates anomalies in Wilson's 

 list. The following conclusions then can be applied only within the 

 limits of the investigation. 



Mesenteric filaments are present, with the single exception of 

 Renilla, throughout the siphonozooids of the more primitive genera, 

 that is in those genera where autozooids and siphonozooids occur 

 together on the rachis, or where the autozooids are arranged in 

 very primitive leaves : — 



lltuaria • funiculina 



Veretillum Protoptilum 



Cavernularia Chunella 



actinoptilum umbellula 



Echinoptilum Osteocella 



kophobelemnon pavonaria 



sclerobelemnon anthoptilum 



In the Virgularias however the filaments are not developed in any 

 species except V. Schultzei which is unique in the genus in having 

 the siphonozooids on the leaves. In the genus Pennatula, the 

 filaments were present in every species examined except P. 

 Murrayi. For Leioptilum and Pteroeides no general statement can 

 be made : the filaments are present in some zooids and not in 

 others. In the latter genus the majority of species are without 

 filaments in the siphonozooids, their presence being noted only in 

 two. In Acanthoptilum, Sarcophyllum and Scy tedium the filaments 

 are entirely absent so far as these genera have been investigated. 



A complete list of species examined will be found at the end of 

 this paper. • 



Function of the Dorsal Mesenteric Filaments. 



It has been shown that the ventral siphonoglyph of the siphono- 

 zooids produces inhalent currents of water into the canal system of 

 the colony (Hickson 1883, Wilson 1884). The dorsal filaments on 

 the other hand produce a current in the opposite direction, i.e. 

 exhalent. Wilson suggests that the circulation thus set up is for 

 the distribution of food (nutritive fluid) amongst the zooids of the 

 colony (I.e. p. 16) . It is probable also that the circulation is for the 

 purpose of keeping up active respiration in the colony. That the 



