June 7, 1900] 



NA JURE 



23 



and the remainder to the Sponges. The Meso- 

 zoa are classified provisionally under four divisions : — 

 (i) Mcsoccflia for Salinella; (2) Mesenchymia for Tri- 

 chophix and Treptoplax ; (3) Mesogonia for Dicyemidae 

 (parasitic in the renal sacs of dibranchiate Cephalopods) 

 and Orthoncctidac (parasites of Nemertines, Ophiurids 

 and Polychaets) ; (4) Mesogastria for Pemmatodiscus. 



Salinella has been regarded as the inoarnation of an 

 ideal proinorph, the true Mesozoon, or link between uni- 

 cellular and multicellular animals. The minute creature 

 which has been saddled with so grave a responsibility 

 was found, in 1892, by the late Dr. Frenzel in a jar of 

 2 per cent, salt solution containing mud taken from the 

 salt works of Cordoba, in the Argentine Republic. The 

 jar had been exposed for a long time, and some iodine 

 washings had been thrown into it by mistake. The 

 authors of the " Traite " give a full account of Salinella, 

 and admit that, if it really exists, "c'est le vrai Meso- 

 zoaire." 



When the complex character of the structure and life- 

 history of the higher Protozoa is considered, the imputed 

 simplicity of Salinella becomes almost grotesque, and it 

 seems impossible to assign a cosmic importance to it, 

 even should its autonomy become, in future years, an 

 established fact. , 



"On ne le dit pas, mais il r^gne une certaine mefiance 

 vis-k-vis de cet etre venu si a propos, recueilli dans des 

 conditions si etranges, observe si loin de nous et une 

 seule fois. Ce vase contenant un liquideartificiel, expos^ 

 a I'air et aux poussieres, qui a recu les ringures de la 

 verrene d'une table d'histologiste, ce pays lointain, tout 

 cela ne prouve rien d'une maniere positive contre la 

 Salinelle." 



Trichoplax and Treptoplax are likewise aquarium- 

 products, the former having been found at Trieste, in 

 1883, by Prof. F. E. Schulze, and the latter at Naples, 

 in 1892, by Prof. F. S. Monticelli. These forms, which 

 superficially resemble an accElous Turbellarian, are riddles 

 of the aquarium, like Salinella in this respect, and it 

 seems premature to draw far-reaching conclusions from 

 them until they are themselves solved. 



The authors of the "Traite" introduce new matter 

 into their account of the Mesogonia derived from a work 

 written in Russian by N. A. Keppen, in which the sper- 

 matozoa of Dicyema are described and figured for the 

 first time. Attention is drawn to the mystery surround- 

 ing the dissemination of the Dicyemid parasites from 

 one host to another, since it is only the infusoriform 

 males which can endure immersion in sea-water, this 

 being quickly fatal to the vermiform females. 



Pemviaiodiscus is a gastruliform organism found by 

 Monticelli (1895), living in closed sacs m the jelly of a 

 Medusa, Rhisostoina pulmo. It would no doubt have 

 excited enthusiasm twenty years ago. Its right to be 

 regarded as an independent type is founded upon three 

 considerations, namely, its parasitic habit, its inability to 

 endure immersion in sea-water, and its power of multiply- 

 ing by division. The first and last of these reasons are 

 by no means conclusive, since parasitic larv;e, as well as 

 embryos contained in brood-pouches, are known among 

 Medusiie, as is also the phenomenon of embryonic 

 fission. 



An account of Haeckel's Gastr^eadcC is given on pp. 38 

 NO. I 5^ 7, VOL. 62] 



and 39, by way of appendix. One might almost have 

 expected to find that the apocryphal Physemaria would 

 have been allowed to go the way of Bathyhius and 

 Eozoon. 



A second appendix (pp. 40-45) is devoted to the ciliated 

 urns found in the body-cavity of Sipunculids. These are 

 regarded by M. M. Kunstler and Gruvel, whose original 

 drawings are here published for the first time, as being 

 certainly parasites, and not forming part of the organisa- 

 tion of the Sipunculid. Two genera are described, 

 Kunstleria n.g. from Phymosoma ; and PompholyxiUy 

 Fabre-Domergue, from Sipiinculus. 



In their treatment of the Sponges, the authors tread on 

 firmer ground, and the result of their labours is a most 

 satisfactory performance. .•\s promorph (type morpho- 

 logique) of the entire group, they select for preliminary 

 description the Olynthus of Haeckel. Olynthus is 

 a generalised abstraction which has its embodiment in 

 concrete zoology. Admitting that a treatise on Sponges 

 at present could hardly be introduced in any other 

 way, it may be pointed out that there are reasons for 

 doubting whether the phyletic value of the Olynthus is 

 as great as its undoubted morphological and didactic 

 importance. 



In the section devoted to the calcareous sponges 

 (pp. 66-82), the authors quote freely from the researches 

 of our compatriots, Prof. E. A. Minchin and Mr. G. P. 

 Bidder. The classification recently suggested by Bidder 

 is given in extenso on p. 67, although not adopted in the 

 body of the work. 



The sextets of actinoblasts which secrete the triradiate 

 spicules of Ascons, as discovered and described by 

 Minchin, are duly recorded, but the figure reproduced on 

 p. 67 gives no idea of the excellence of the illustrations 

 contained in Minchin's monograph. 



The complete inversion of the layers, which takes 

 place at the metamorphosis (pp. 60, 69, 106, 159), marks 

 one of the most interesting phases of sponge-life. The 

 primitive endoderm of the larva gives rise to the per- 

 manent epidermis of the adult, while the primitive 

 flagellated ectoderm sinks in to form the flagellated 

 chambers of the adult. This fact of inversion has induced 

 Delage to separate the Sponges, under the designation 

 Enantiozoa, from all other Metazoa. 



The metamorphosis of the parenchymula-larva is 

 accompanied by phenomena which have an interest ex- 

 tending beyond the limits of sponge-lore. The account 

 given on pp. iio-iii shows the following succession of 

 events which occurs in some cases during the conversion 

 of the flagellated ectoderm of the larva into the choano- 

 cytes (collar-cells) of the adult : — 



Flagellated 

 Ectoderm. 



II. 

 Histolysed 

 Ectoderm. 



III. 

 Syncytial 

 Ectoderm. 



IV. 



Choanocytes. 



The reconstructions on the coloured plates, which 

 elucidate the increasing complexity of the inhalent and 

 exhalent canal systems throughout the group, are well 

 executed, and produce a satisfying impression of solidity 

 and reality. If there is a complaint to be made, it is 

 that, in not a few cases, the authors have omitted to add 

 in brackets the name of the generic type to which the 

 diagrams and text-figures may be taken to refer. 



Textual errors and inconsistencies are rare, and obvious 



