462 RECORD OF CURRENT RESEARCHES RELATING TO 



Internodes in Sertularians.* — Taking Sertularia pumila Linn, as 

 the first example in which to show the modifications which these parts 

 may undergo, G. Winther finds that in this species the rule which assigns 

 a joint to the stem between each two pairs of internodes, is liable to 

 many exceptions. This joint is often more or less obliterated, e. g. in 

 the lower part of the stem ; a thickening of stem occurring in its place : 

 higher up in the stem the parts are all more slender and the joints 

 more conspicuous than below. Again, instead of having two hydro- 

 thecae only, the internode may bear four, and is then described as an 

 internode of the second order. Typically, the upper third of the 

 hydrotheca is free, and makes an angle with the rest, but the younger 

 and more slender is the internode, the more nearly parallel are the 

 two hydrothecfe ; while near the root the upper part of the internode 

 between the cells becomes broader, deflecting these to the sides, so 

 that they form a large angle with their bases ; this dilatation in time 

 reaches the lower part of the internodes. 



The bending and freedom of the upper end of the cell are not due 

 to its growth at this part. 



In Sertularia gracilis Hassall, the form of the internode is 

 not a fixed one ; though in general it is longer and more slender 

 than that of S. pumila ; but examples high up on the stem may excel 

 thick ones of that si)ecies. Here, too, it is the greater or less freedom 

 of the parts composing the joints which affects the slenderness of the 

 internode. The breadth of the joints has no significance as a 

 character, as it varies with the internodes. Variations from the bi- 

 celled arrangement are less frequent than in S. pumila. The flexion 

 of the hydrotheca is greater and the stem is thinner than in that 

 species ; facts probably due to the slighter build and consequent 

 greater pliability of the parts. It is the amount of projection of the 

 hydrothecaB which distinguishes the species. By way of formulating 

 the dift'erences between the two, it may be stated that the tendency of 

 S. pumila is to enclose more hydrothecfe by excessive development of 

 the stem ; in S. gracilis, for these to remain unaffected by that part. 



In Sertularia cupressina Linn., an internode carries as a rule 

 six calycles, therefore it is of the third order. But internodes 

 of the second or of the fourth (with eight calycles) order may occur ; 

 or in some colonies first order internodes may aj^pear. But this 

 species is fundamentally distinct from the two-celled S. pumila in the 

 alternating arrangement of the calycles on the stem ; they being oppo- 

 site each other in that species. Owing to this alternating position the 

 cells are not laterally deflected with age. 



S. tenera Sars presents great affinities with the preceding form. 

 There is a considerable distance between the pairs of calycles, and 

 second order internodes are the typical arrangement. They may be 

 preceded by those of the first order, and a parallel branch may show 

 some of the third order ; but the thickness and shortness of the stem 

 increase with the number of cells. The thickness of all parts of S. 

 tenera is always less than half that of S. cupressina. A special feature 

 of the species is the intercalation, chiefly singly, of small bare joints 

 * ' Nat. Tiddsk.,' xii, (1879) }>. 303. 



