HISTORY. 67 



animal, placed one of them in water, and, after some weeks, had the pleasure of seeing escape 

 from it a minute polypoid animal, which he recognised as that figured and described by Rusel, 

 and afterwards, under the name of CristatcUa, assumed as the type of a new genus by Cuvier. 

 Turpin describes the bodies from which these little animals proceeded with considerable detail, 

 but his account is in many respects erroneous. He alludes to the annulus with which they 

 are surrounded, but sets this appearance down as the result of an optical deception, and he 

 incorrectly describes their curious hooked spines as, for the most part, growing from the extreme 

 margin ; while he tells us that the bodies in question open in a plain perpendicular to the two 

 faces, to allow of the escape of the young one, instead of having the plane of dehiscence, as is 

 really the case, parallel to the faces. He is at first at a loss to explain how such formidably 

 armed " eggs " could be brought forth with impunity, and he asks : " Quelle pouvait etre la 

 malheureuse mere condamne a contenir et surtout k pondre des ceufs aussi horriblement herisses 

 de crochets V He afterwards, however, finds an explanation of the difiiculty, for seeing the 

 feeces expelled in the form of oval masses, he mistakes these masses for eggs, and thence con- 

 cludes that the eggs are at first free from spines, and acquire this armature only after being 

 laid. M. Turpin gives a very beautiful figure of the young animal, which he describes with 

 great care, though, not having the advantage of adult or of sufficiently numerous specimens, 

 his account is in some respects erroneous. 



The same year, M. Gervais published another memoir on the fresh-water Polyzoa.* In 

 this memoir he constitutes a distinct genus, under the name of PaludiceUa, for Ehrenberg's 

 Alryonella articulata; and he further makes an important step in the classification of the 

 Polyzoa, dividing them into two subordinate groups, PoJypiaria hippocrepia and Polypiaria 

 infundihidata, the former being constituted for those with the tentacula upon the margin of a 

 horseshoe-shaped disc, and including all the fresh-water species except PaludiceUa and 

 Fredericella ( = Tuhularia sultana, Blumenbach), which, in consequence of having the tentacula 

 arranged on a circular disc, Gervais unites with the marine Polyzoa, to constitute the group 

 Polypiaria infundihulata. We have already seen that De Blaiuville was impressed with the 

 necessity of this division, and established his Polypiaria dubia, corresponding with Gervais's 

 P. hippocrepia, to meet it ; but De Blainville's group, including certain animals which are 

 manifestly incorrectly placed there, required the revision introduced by Gervais. Gervais now 

 corrects the erroneous description of the egg (statoblast) given by Turpin, but he tells us no 

 new fact of importance concerning the animal, and he commits the serious error of uniting all 

 the other species with crescentic discs under the single one of Plumatclla campamdata. 



About the same time, M. Turpin read to the Academy of Sciences a memoir on certain 

 microscopic organized bodies which he found enveloped in some varieties of opal.f In these, 

 he recognises so much similarity with the statoblasts of the CristatcUa, with whose study he 

 had just been engaged, that he does not hesitate to consider them as the eggs of some nearly 

 allied animal. The fossils, however, thus attempted to be determined by Turpin, have nothing 



* Gervais, Recherches sur les Polypes d'eau douce des genres Plumaiella, Cristatella, et Paludi- 

 ceUa. ' Aun. Sc. Nat./ 2' ser., vii, 1837. 



f Turpin, Analyse ou Etude microscopique des different corps organises et autres corps de nature 

 diverse qui peuvent accidentellement se trouver enveloppes daus la pate trauslucide des Siles. ' Acad. 

 Sc. Paris/ Mars, 1837. 



