Professor Herdman on the Structure of Sarcodictyon. 49 



polypes. Such a condition is shown on PL I. in Fig 2. 

 and at the right-hand end of Fig. 1 ; and this seems to unite 

 the first characteristic of Forbes' Sarcodictyon agglomerata, with 

 the other features of S. catenates Then the second characteristic 

 of S. agglomeratct is, of course, seen in my yellow variety of 

 S. catenata. Hence, if Sarcodictyon agglomerata is really a 

 distinct species from >S^. catenata, it will require to be care- 

 fully examined and redescribed; and I have shown above that 

 Pourtales' S. rugosum is insufficiently characterised, and does 

 not seem from the published description to differ from the 

 British species. Consequently there is, so far as I am aware, 

 only one well-marked species of Sarcodictyon known to 

 science. 



Explanation of the Plates. 



The following objectives have been used while drawing 

 the figures ; — 



Swift, 1 incli, magnifies 45 times. 

 „ i „ „ 225 „ 



,. * „ ,, 300 ,, 



Zeiss, iV oil-immersion, magnifies 

 950 times. 



The following system of lettering has been adhered to 

 throughout : — 



eras., craspedum. 



<nct., cuticle. 



ec, ectoderm. 



ec. cce., ectodermal cseca. 



en., endoderm. 



en. cce., endodermal creca or 



tubules. 

 g. t., gastric tube. 

 i. my., intermesenteric chamber. 

 i. t. , invaginated tube. 

 lac, lacuna in mesoderm. 

 lo. , lobe, 

 m., mouth. 



mes., mesoderm. 



7n. f. c. , circular muscular fibres. 



m. f. I. , longitudinal muscular fibres. 



m. my., mesenteric muscles. 



my., mesentery. 



n. c, nerve cells. 



nem., nematocyst. 



2)., polype. 



sp., spicule. 



St., stolon. 



in., tentacle. 



tn. XJ. , pinna of tentacle. 



PLATE L 



Fig. 1. A colony of Sarcodictyon catenata (Forbes), red variety, — natural 

 size. 



Fig. 2. Part of another colony, showing several polypes on a common ex- 

 panded stolon, — natural size. 



Fig. 3. Part of another colony with rather a thick stolon, — natural size. 

 VOL. VIIL r> 



