HYDROIDA 



57 



transverse belts. This peculiarity we find slightly indicated even in some Bougainmlliidae. But only 

 in the Eudendriidae it has become a character plainly distinctive. Further, the endoderm in the well 

 defined hypostome shows the same structure as in the thecaphore hydroids, and is more strongly differ- 

 entiated than in the Bougain'villiidae, the indifferent cells having gained the ascendency, and the number 

 of the mucous gland cells having been reduced to a minimum. Whether these peculiarities are indic- 

 ative of a nearer relationship between the Eudendriidae and the thecaphore hydroids, is a question 

 which it would here be out of place to enlarge upon. 



The Eudendriidae^ with their frequently dimorphic development of the stinging cells, also pre- 

 sent a parallel to the Stylasteridae. Besides the small rodformed stinging cells characteristic of all 

 rilifcra, we also find in several species larger narrowly oval ones, bearing a strong resemblance to 

 those of the Stylasteridae. The latter are large, but of the same shape as the small stinging cells of 

 Myriothcla. We probably here face a phenomenon of convergency, the reason of which, however, at 

 the present stage of our knowledge of the biology of the Coelenterata, we cannot account for with 

 any certainty. Wherever the larger stinging cells occur in the Eudendriidae they are accumulated in 

 particular stinging organs. 



Eudendrium Ehrenberg. 



Upright colonies with branched hydrocaulus. The polyps are broad and distinctly set off from 

 the stem, which is covered with a vigorous chitinous perisarc. The polyp has a single whorl of fili- 

 form tentacles. Above the tentacle whorl the polyp is suddenly tapering and ends into a capitate or 

 trumpetshaped proboscis, which is seated, with a narrow base, above the tentacle whorl. The gono- 

 phores are developed on normal or reduced polyps, or placed singly on the branches. 



Kiihn (1913, p. 48) states that the polyp tentacles of Eudendrium "nach einander vorsprossen 

 und dadurch sich als Angehorige verschiedener Wirtel zu erkennen geben". Later on (1. c. p. 247) he 

 again mentions this peculiarity as a refutatory argument against the adoption of a nearer relationship 

 to the thecaphore hydroids; in the passage last quoted he apparently bases his opinion essentially on All- 

 man (1872). A closer inquiry, on new material, gave no hold to the statement of A 11 man and Kuh n that 

 the tentacles should appear successively. In the numerous colonies examined of Eudendrium rameum 

 (Pallas) and Eudendrium Wrighti Hartlaub it could be ascertained that all the tentacles appear 

 simultaneously. This suggests that the observations of All man may rather depend on accidental cir- 

 cumstances, and that no special importance must be attached to them as reminiscences of manyrowed 

 tentacle-whorls of the ancestors or as proofs of a nearer or remoter relationship to the Bougainvil- 

 liidae or to the thecaphore hydroids. 



Eudendrium rameum (Pallas) Thompson. 



1766 Tubularia ramea, Pallas, Elenchus zoophytorum, p. 83. 



1844 Eudendrium rameum, Thompson, Report on the Fauna of Ireland, p. 283. 



1887 ramosum, Bergh, Karahavets goplepolyper, p. 332. 



8 



The Ingolf-Expedition. V. 6. 



