HISTORY, 71 



In the same year, MM. Dumorticr and Van Bencden presented, conjointly, to the Iloyal 

 Academy of Sciences at Brussels, a second and very important memoir on the ' Natural History 

 of the fresh-water Polyzoa.' * This memoir is occupied with the anatomy of the genera 

 Paludicclla, Fredcricella, AlcyoneUa, and Lophopus, and accompanied by numerous well- 

 executed figures. It contains extensive and careful anatomical details of all the genera 

 treated of in the memoir. It describes and figures with much minuteness the development of 

 the bud in Paludicella, and mentions the occurrence of a peculiar winter bud in this Polyzoon, 

 occupying the position of the ordinary buds,' but destined to remain during the winter months 

 in an undeveloped state. The structure of the testicle in AlcyoncUa is examined, and the 

 spermatozoa, with their vesicles of evolution, demonstrated ; but these cells are not sufficiently 

 distinguished from the contained spermatozoon. The ciliated embryos of Alcyonella are also 

 described and figured, but the authors do not pursue their development into much detail, while 

 they consider them as identical with statoblasts in a particular stage of evolution, and deprived 

 of their external shell. The statoblasts themselves in Ahyonella and Fredcricella are described, 

 but the essential structure of an ovum is attributed to them, while some confusion has arisen 

 with regard to the statoblast of Loiihopus crystallinus, the body described as such being mani- 

 festly the statoblast of CristatelJa. A statement formerly made by M. Dumortier, that the 

 tentacula of Lophopus crystallinus are deprived of cilia, is repeated here ; it is asserted that, 

 instead of ciliary vibrations, the tentacula of this Polyzoon present a moniliform current, which 

 ascends one side and descends the other of each tentacle ; the appearance of these currents is 

 compared to that of an endless chain in uninterrupted motion, and attention is drawn to the 

 analogy of this phenomenon with that of the decomposition of water by the galvanic battery. I 

 have no doubt, however, that the phenomenon thus described is truly a case of ciliary vibra- 

 tion, and that the cilia have merely escaped the observer in consequence of some defect in the 

 microscope employed in their investigation. I have repeatedly had under my own observation 

 a species of Lophoims, which I do not hesitate to refer to M. Dumortier's species, and yet 

 I found the cilia in all cases perfectly distinct. An opinion previously expressed by M. Van 

 Beneden, when he thought he had seen apertures (" bouches aquiferes") for the admission of 

 water into the perigastric space, is here given up, and the source of the error pointed out. 

 Further, M. Van Beneden, now finding a testicle in the same cell with the statoblasts, modifies 

 his previous views as to the unisexualism of Alcyonella, and, comparing this Polyzoon to the 

 plants belonging to the twenty-third class of Linnceus, he suggests that male, female, and 

 hermaphrodite individuals may all coexist in the same coenoecium. On the whole, this 

 memoir of the learned Belgian naturalists, though in some respects incorrect, must be regarded 

 as the most important, in an anatomical point of view, of any which had as yet appeared. 



In the same year (1848), Sir J. G. Dalyell published the second volume of his ' Rare and 

 Remarkable Animals of Scotland, '•j' and described in this work several species of fresh-water 

 Polyzoa, as inhabitants of that part of the British Islands. Dalyell is a truthful observer 

 and a graphical describer of the habits of the lower invertebrate animals, but he is not 



* DuMouTiER et Van Beneden, Hist. Nat. des Polypes composes d'eau douce, 2'^ partie. Coqi- 

 plement au tome xvi des 'Mem. de I'Acad. Roy. des Sciences et Belles-lettres de Bruxelles/ 1848. 



t Dalyell, ' Rare and Remarkable Animals of Scotland, represented from living subjects.' Lou- 

 don, 1817-8. 



