Professor Herdman on the Structttre of Sarcodictyon. 35 



III. Structural. 



A colony of Sarcodictyon catenata presents the appearance 

 of a narrow band, the stolon, adhering to the surface of a 

 stone or fragment of shell, and bearing at intervals conical 

 enlargements, the polypes.^ 



The Stolon is flattened from above downwards so as to form 

 a comparatively thin crust closely attached to the stone or 

 shell. It is thickest in the middle of its breadth, and thin 

 at the edges, so that in section its upper surface is convex. 

 Most of the pieces of stolon which I have measured are from 

 1*5 to 2 mm. in breadth, a few are narrower or broader. In 

 some cases I have found free tips of stolons not connecting 

 polypes, which were tapering and very thin. These were 

 clearly growing points. They were of a paler colour than 

 the rest, being almost colourless in the red variety, and quite 

 colourless in the yellow variety. 



In a few cases (see right-hand end of PL I., Fig. 1) the 

 stolon is enlarged at its edges to form an expansion of con- 

 siderable breadth, which may even occasionally (PL I., Fig. 2) 

 support several polypes side by side. Hence the polypes are not 

 always placed in a single series. Such a case appears not to 

 have been met with by Mr Hickson, and it seems to supply 

 a link in his chain leading up to an expanded lamellar stolon 

 underlying all the polypes of a colony, as in the case of 

 Tubipora.^ Its bearing upon Forbes' Sarcodictyon agglo- 

 merata I shall discuss later on. 



The stolon expands slightly as it approaches the base of a 

 polype, and is usually narrowest half-way between two 

 polypes. The stolons branch frequently, but always at the 

 base of a polype, a branch never being given off between two 

 polypes. They also anastomose, the points of union being 

 again. always at a polype, so that in the networks formed 



1 The colonies I have examined vary in the number of their polypes from 

 3 to about 150. Gosse {loc. ciL, p. 276) speaks of some polypes as being 

 isolated. I have not met with any in that condition. My colonies number 

 as follows :— Yellow variety, Loch Fyne, 12 and 14 polypes; red variety, 

 Loch Fyne, 3, 4, 9, 17, 50, 120, and 150 ; red variety, Lamlash, 30, 32, 35, 

 37, 50, 77, and a few others not counted. 



2 Quart. Jour. Micro. Science, vol. xxiii., No. xcii., p. 576, 1883. 



