148 ANNALS NEW YORK ACADEMY OF SCIENCES 



becomes rather difficult to keep those of the two sides distinct, on ac- 

 count of the shape and density of the branches. 



Mode of Life of Dictyonema flabelliforme 



Writers differ greatly in their opinion regarding the mode of life of 

 Dictyonema flabelliforme, one considering it planctonic, another ben- 

 thonic, but in recent years the idea of an epiplanctonic 22 life, i. e., by 

 adhesion to floating seaweed, has been introduced with success by Wal- 

 ther and Lap worth. Even, however, in the case of Dictyonema, where 

 among the Dendroidea the epiplanctonic theory might possibly have 

 applied, an earnest objection was raised by Wiman when he showed that 

 D. cavemosum had branching stolons, partly strengthened by radial ribs, 

 leading him, as it did Jaekel before him, to the conclusion that this spe- 

 cies, like the "sessile denizens of the deeper regions," must have formed 

 meadows on the bottom. Matthew found at Navy Island two mature 

 forms, each with a distinct rootlet, and yet he made the suggestion that 

 "possibly these processes may have had some other office than that of 

 anchoring." Euedemann, agreeing with him, lays special stress on the 

 fact that all well-preserved specimens from Schaghticoke, whenever re- 

 taining more than the sicula, were provided with long thin nemas. Thus 

 he is inclined to assume a suspended life for Dictyonema flabelliforme, 

 with fixation in old stages, as unimportant exceptions. Eecently, Wester- 

 gard, to whom we owe the best work on the Swedish material, completely 

 disregards the indications of what was called a "rootlet," stating that 

 among one hundred specimens no nema and no disk has been observed 

 in spite of distinct proximal parts exhibiting free sicuke. 



With these contradictory facts in mind, when studying the Columbia 

 collection, which fortunately preserves the two known examples of root- 

 lets, I proceeded to investigate all the available material with the fol- 

 lowing results : Of 500 specimens part way through the first stages of 

 growth, only 20 per cent have a well-preserved sicula, which even in 

 ephibastic stages ends, as a rule, in a sharp point ; a few specimens, most 

 of which are not quite ephebastic, are provided with a nema as in Euede- 

 mann's examples and I observed only three nemas up to 20 mm. in 

 length; the younger the stages, the more individuals possess nemas; 

 78 per cent have a more or less broken or concealed end, about 2 per cent 

 other basal organs. 



In order to present a fair account of the last, I have tried to draw all 

 the examples in question with most careful accuracy. (Plate XXL) 



22 Walther used the term pseudoplancton ; the term epiplancton has been introduced 

 by Grabau to cover organisms living on or attached to pseudoplancton. 



