The early development of Eudendrium. 273- 



planulae of Pennaria, where it is described and figured, so that no 

 special account of the phenomenon is necessary here, since it seems 

 to be quite similar if not identical in the two. Sections of such 

 planulae show that the bifurcation involves both ectoderm and ento- 

 derm and gastric cavity as well. 



The fixation of the planula and development of the hydranth 

 usually occurs within two or three days, tho it is sometimes, in 

 specimens reared in small aquaria, considerably defered. As the 

 period of fixation approaches the larval movement become less 

 active , indeed rather sluggish ; heliotropism largely disappears, or 

 becomes negative in character. Finally the planula settled upon 

 its broader, or ôboral pole, fixes itself by a slimy secretion upon 

 the bottom of the aquarium, or some fragment of sea-weed', or 

 other support and finally ensheaths itself wholly within a delicate 

 perisarc, which, like that of Pennaria, and probably most hydroid 

 planulae, is so very delicate and transparent as often to escape notice. 

 Then ensues a period of several hours, probably twelve to twenty- 

 four, of quiescence, during which final metamorphosis into the young 

 hydroid occurs. Excellent figures of these phases are given in 

 Allman's Gymnoblastic Hydroids, tab. 13, figs. 11 — 16. With the 

 budding of the tentacles the young hydranth ruptures or dissolves, 

 the terminal perisarc obtrudes itself, expands its tentacles, having 

 in the meantime acquired a mouth, and begins the serious struggle 

 for existence. 



Naples, June 23, 1903. 



Literature. 



Allen, C. M., The development of Tubularia crocea, in: Biol. Bull., 



V. 1, 1900. 

 Allmax, J. G., A Monograph of the Gymnoblastic Hydroids, London, 



1871. 

 Braukr, a., Ueber die Entstehung der Geschlechtsprodukte und die 



Entwicklung von Tubularia mesembryanthemum, in : Z. wiss. Zool., 



V. 52, 1891. 

 Cavolini, J., Memorie per servire alla storia de'Polipi marini, Napoli 1785. 

 CoE, W. R., Maturation and early development of Cerebi'atulus, in : 



Zool. Jahrb., V. 12, Anat., 1898. 



