Manchester Memoirs, Vol. Ixii, (191 7) No. 4 7 



leaves which bear the siphonozooids have little muscular tissue 

 whose contraction could drive the water out from the colony ; 

 filaments are therefore present to serve this function. In other 

 species of Virgularia contractions of the rachis doubtless serve to 

 eject the water which has been inhaled by the siphonozooids. 



In some species of Umbellula siphonozooids are recorded in the 

 basal bulb of the colony. It is not established beyond doubt that 

 these possess mesenteric filaments, but if their presence be estab- 

 lished it would be in accordance with the general statement made 

 above. There is no reason to doubt that respiration goes on in 

 this part of the colony, even if the normal position is buried in the 

 sea-bottom mud or sand, and mesenteric filaments would promote 

 the circulation of water in this fleshy region as in the tassel at the 

 distal end, while the intermediate zooids of the very slender rachis 

 would not require filaments. 



Finally it may be suggested that in some cases it would be 

 advantageous to use the presence or absence of dorsal mesenteric 

 filaments as a character for classification. There is no reason to 

 suppose that this anatomical character is not constant for a given 

 species, and in cases where local environmental conditions produced 

 some modification or variation in external character it might prove 

 a valuable guide in identification. 



Notes on Mesenteric Filaments. 



Lituaria Hicksoni. Thomson and Simpson. 



Siphonozooids mounted whole and viewed from the surface or 

 from below showed no indication of filaments but transverse 

 sections through the zooids shewed them to be present in every 

 zooid. The average width was 0.048 m.m; most of the filaments 

 were very definitely Y-shaped in section, but others which did not 

 appear well preserved were more rounded and the medium groove 

 was not well marked. 



Veretillum malayense. Hickson. 



Siphonozooids mounted whole showed no indication of mesen- 

 teric filaments. The specimen viewed externally seemed to be well 

 preserved but the internal tissues were not in a sufficient state of 

 preservation to determine whether filaments were present or not. 

 In longitudinal section there were signs of cells in continuation 

 from the stomodaeum but the characteristic structure of filaments 

 was not evident. 



