2 Lightbown, Filaments in the Siphonozooids of Pennatulacea 



This statement however, as recently pointed out by Professor 



Hickson, does not cover the whole facts of the case. "Since that 



'date Niedermeyer (1911, p. 36) has stated he could not find the 



'mesenteric filaments of Pteroeides griseum. On examining" a 



'series of preparations of Pt. malayense, Pt. caledonicum, Pt. 



't.imorense, and Pt. argenteum, I could find no trace of dorsal 



'mesenteric filaments, but in a similar preparation of Pt. 



'Steenstrupii they were present and of considerable size. In the 



'genus Pteroeides therefore they are sometimes present and some- 



' times absent. This is also true for Umbellula and Pennatula. In 



'the large siphonozooids of the petaloid areas of U. Carpenteri 



'these filaments are present and well developed but in the small 



'siphonozooids of the stem and stalk they are absent. In the 



'siphonozooids of Pennatula phosphor ea (Marshall 1882, p. 46) 



'they are present and also in those of P. grandis but in the 



'siphonozooids of P. Murrayi they are absent." (Hickson 1916, 



p. 10). Mesenteric filaments have been recorded for a few other 



isolated species by recent writers as noted in the text of this 



paper. 



This research therefore was undertaken to investigate the dis- 

 tribution of these filaments in the siphonozooids of the order 

 Pennatulacea. For this purpose Professor S. J. Hickson most 

 kindly placed at my disposal the whole of his preparations of the 

 Pennatulacea from the Dutch "Sihoga^ Expedition and many 

 specimens from his private collection. 



Methods. 



In all species the siphonozooids were first examined whole, by 

 cutting out a piece of the body wall or leaf and dissecting away the 

 underlying tissue, slowly decalcifying in a weak solution of nitric 

 acid in 70 per cent alcohol, and staining with Grenacher's haema- 

 toxylin. Where further examination was required transverse or 

 longitudinal serial sections (5ju — 6ju thickness) of the siphono- 

 zooids were made, and in these also Grenacher's haematoxylin was 

 found to give the best results. In many species, notably in those of 

 Anthoptilum, sections in which this stain was used snowed a dis- 

 tinct double stain when washed in acid alcohol, the ectoderm of 

 the stomodaeum and filaments appearing bright red, all other 

 endodermal and mesodermal tissues bluish purple. This red stain 

 however faded to a uniform purple on neutralising with alkaline 

 alcohol, or even on exposure to sunlight ; hence, in most of the 

 permanent preparations the mesenteric filaments are not so strik- 

 ingly contrasted with other structures as at the first examination. 



