March 6, 1879] 



NATURE 



407 



canals disposed around a central axis, has received 

 abundant confirmation. 



The curious genus Rhopaladina has been supposed by 

 some writers to be the type of a new group of Echino- 

 derms, with mouth, anus, and genital opening at the 

 centre of one of the poles of the body. Ludwig shows, 

 however, that it is merely an aberrant Holothurian, much 

 bent on itself, owing to the almost complete disappear- 

 ance of the medio-dorsal inter-radius, an exaggeration, 

 in fact, of a condition very commonly met with in Cucu- 

 maria. Ludwig' s memoirs on the Asterids contain several 

 novelties, two of the most important of which are as 

 follows : — 



1. The pores in the madreporic plate have no com- 

 munication with the ccelom, but lead solely into the 

 sand canal. The same fact has been noted by Perrier 

 for the Echini, and it is the more singular because the 



body cavity of the Crinoids is in free conamunication with 

 the exterior. 



2. The genital glands do not discharge their products 

 into the body cavity, but are provided with longer or 

 shorter ducts that open directly on the exterior of the 

 body. Around the glands are blood spaces, just as in the 

 Crinoids, and these are connected with a very complicated 

 blood-vascular system, which Dr. Ludwig describes ex- 

 ceedingly well, clearing up many points which had 

 hitherto been very obscure and scarcely understood. This 

 is especially the case with the remarkable genus Brisinga, 

 which Sars supposed to be without a blood- vascular sys- 

 tem. Ludwig contributes many valuable observations to 

 the anatomy of this type, and shows that in all essential 

 features it is a true Asterid, though he does not share Sars' 

 ■ iews of its relationship to Protaster. 



The volume closes with a striking paper on the 

 Ophiurids, in which it is shown that the whole of the oral 

 skeleton of the disc is the result of modifications of the 

 first two arm-vertebrae and of the adambulacral and super- 

 ambulacral plates corresponding to them. But the chief 

 novelty in this paper relates to the genital clefts. These 

 have been hitherto supposed not only to let the genital 

 products pass out of the coelom,', but also to admit water 

 into it. Ludwig shows, however, just as in the case of 

 the Asterids, that both these hypotheses are incorrect. 

 The sexual products are not discharged into the ccelom, 

 nor does water enter it by the clefts, but the latter open 

 into pouches or bursae which are merely involutions of 

 the general integument of the body, and receive the short 

 ducts of the genital glands, probably serving also as a 

 respiratory apparatus. Their inner surface, that turned 

 towards the ccelom, is curiously folded, and their whole 

 structure is so very similar to that of the hydrospires of 

 the Blastoidea that Ludwig is led to suggest a homology 

 between these two sets of similarly placed organs. 

 Billings considered the hydrospires to be respiratory in 

 function, and found them to be connected with the 

 "spiracles" or genital openings, which would thus be 

 homologous with the genital, or, as Ludwig prefers to call 

 them, "bursal" clefts of the Ophiurids. 



Should further investigation confirm this interesting 

 discovery of Ludwig's, and the conclusions he has drawn 

 from it, we quite agree with him in regarding it as one 

 of great importance respecting the relations of the various 

 echinoderms inter se. 



We shall look with great interest for the publication of 

 Dr. Ludwig's promised researches on the Echini and 

 Holothurians at, we trust, no distant time ; and also for 

 his concluding work on the comparative morphology of 

 the sub-kingdom as a whole, which will not, we imagine, 

 be altogether a pillar of strength to Haeckel's celebrated 

 " Worm Theory of the Echinoderms." 



OUR BOOK SHELF 



yornal de Sciencios Mathematicas I^hysicas e Naturaes. 



Publicado sob os auspicios da Academia Real das 



Sciencias de Lisboa. No. xxiii. agosto de 1878. 



(Lisboa, 1878.) 

 Giornale di Matematiche : aduso degli Studenti delle Uni- 



versitcL lialiane, Pubblicato per cura del Professore 



G. Battaglini. Vol. xvi. (Napoli, 1878.) 



We have not seen any previous numbers of the first of these 

 publications, but from the specimen before us we should 

 certainly conclude that this Society is doing good work. In 

 fifty-two octavo pages we have specimens of work in all the 

 lines indicated in the above title. The opening paper, by 

 C. A. Moracs de Almeida, is an " estudo gcral dos es- 

 pelhos curvos " (continuation, 1 1 pages) ; Chapter IV. 

 treats of spherical, elliptical, and parabolical mirrors of 

 very small aperture ; Chapter V. discusses some cases of 

 practical difficulty in the formation of images. The 

 second paper is a mathematical one by L. F. Marrecos 

 Ferreira ; ist part, on the geometrical properties of the 

 intersections of right cones, derived from the principle of 

 the homological transformation ; 2nd part, on the pro- 

 perties of conies tangential to the sides of an angle and 

 their application to the study of surfaces (18 pages). 

 Both papers are neat, and contain interesting properties. 



Zoology follows, with two contributions by J. V. Bar- 

 boza du Bocage, first with a list (the sixteenth) of the 

 birds in the Portuguese possessions in West Africa (15 

 pages), next imder the title "M^anges Omithologiques," 

 remarks on new species of Angola {Nectatinia anchietce^') 

 and on individual birds of the families Certhiida? 

 {Hylypsomis Salvadort), Paridae (Pat us rufiventris), 

 Laniidae {Lanius Sousce, Nilaus affinis). 



The last two pages contain a slight account of iii 

 plants, collected in Caconda by Signor Anchieta. Re- 

 marks are made on the points of contact between some of 

 the plants in this collection and that got together by the 

 late Dr. Welwitsch 



The second journal maintains its reputation for its contri- 

 butions to the study of geometry. WTiere there is so much 

 to praise we must limit ourselves to giving here the bare 

 titles of some of the longer papers : — Ricerche geome- 

 triche sopra alcune proprieta dei sistemi di rette nel piano 

 e dei sistemi di circoli che passano per un punto sul piano 

 e sulla sfera, per T. Fuortes (56 pp.) ; Sulla riforma 

 dell'insegnamento geometrico, nota di G. Fiedler seguita 

 da tre lettere inedite dell' autore (13 pp.) ; Sull' infinitk 

 circolare non Euclidea, per G. Battaglini (7 pp.) ; Re- 

 lazione fra I'area e il perimetro, fra il volume e la super- 

 ficie, fra i momenti, fra le coordinate dei centri di gravitk 

 per gli spazi limitati da linee e superficie che banno 

 I'equidistante della stessa natura per U. Dainelli (20 pp.); 

 Sulla teoria delle quadriche omofocali del pimto di vista 

 sintetico per F. Maglioli (36 pp.) ; Nozioni preliminari 

 per la geometria projettiva dello spazio rigato, Nota i di 

 F. Aschieri (19 pp.) ; Sopra le curve piane del 3° ordine 

 con un punto doppio, per P. Anelli (14 pp.). 



The History of Coal. By the Rev. T. Wiltshire, M.A. 

 F.G.S., &c. (E. and F. N. Spon, Charing Cross and 

 New York. Pp. 36, 1878.) 



This pamphlet is the introductory lecture which the 



I So named frcm the finder, who met with a single specimea, October, 

 1877, in the interior of BenguelJa. 



