877 



SPLEENWORT. 



SPONGIA. 



878 



arterial twigs of considerable size, which may be seen by boiling the 

 Spleen in acidulated water, and cutting it into thin sections. 



The function and structure of the Spleen have been recently 

 studied with great care by Mr. Gray, and his Essay on this subject 

 obtained for him the Astley Cooper prize. He sums up his 

 researches under the following heads : 



1. The Spleen exists without exception in all Vertebrate Animals. 



2. It presents however by far its greatest development of structure, 

 and consequently its function is most perfectly developed, in the 

 Mammalia, this being partly dependent upon the greater general 

 completeness and requirements of their organisation. 



3. Part of the offices of this organ are plainly those of a diverti- 

 culum for blood. This is especially seen in the Diving Animals, 

 where its large size is undoubtedly associated with considerable 

 obstruction to the circulation which takes place under these circum- 

 stances. Its large size also in those animals in which assimilation of 

 food rapidly occurs, and in which, consequently, new material is sud- 

 denly added to the circulation as compared with its extremely dimi- 

 nutive size under the opposite conditions, also affords evidence of its 

 diverticular function. 



4. The total absence in Reptiles and Fishes of one of the main 

 elements of this gland in Mammalia and Birds, is in perfect accord- 

 ance with their low grade of organisation, and the remarkable faculty 

 they possess of sustaining hunger for almost an unlimited period ; 

 whilst in the former they form a ready, although a scanty, sinking 

 fund for albuminous materials that can be rapidly given up to the 

 blood during their temporary and occasional abstinence, and which 

 cannot be borne by them with impunity for any long period. 



5. Its function then is not for specific but for general purposes, 

 serving to regulate under many varied and opposite conditions the 

 quantity and also the quality of the blood. 



SPLEENWORT. [ASPLENICM.] 



SPODU'MENE, Trijihane, a Mineral occurring in imbedded crystal- 

 line masses. Primary form a rhombic prism. Cleavage parallel to 

 the primary faces and to the diagonal planes ; that parallel to the 

 smaller diagonal is most brilliant, and that parallel to the greater 

 most difficult. Fracture uneven, granular. Hardness, scratches 

 glass and gives fire with steel. Colour whitish- and greenish-gray. 

 Streak white. Lustre pearly on the cleavage planes. Specific gravity 

 3'17 to 3'188. Before the blow-pipe it swells and fuses into a glass 

 almost colourless and transparent ; with borax it swells, but does not 

 easily dissolve. 



It is found at Uto in Sweden, in the Tyrol, Ireland, and North 

 America. The analyses of this mineral by Arfwedson from Sweden, 

 by Stromeyer, and I-e Hunt from Ireland, gives the annexed 

 results : 



Arfsrcd.ion. Stromeyer. Le Hunt. 



Silica .... 66-40 63'288 63-812 



Alumina .... 25'30 28776 28'50S 



Lithia .... 8-85 5-626 5-604 



Lime 0-728 



Protoxide of Irou . . 1-45 0-794 0-828 



Protoxide of Manganese . 0-204 



Moisture .... 0'45 0775 0-360 



102-45 99-463 99-840 



SPONDIA'CE^E, a natural order of Plants belonging to the 

 Syncarpous group of Polypetalous Exogens. It has unisexual 

 Sowers; a 5-cleft regular cnlyx ; 5 petals, inserted under the disc; 

 10 perigynous stamens arising from the same part as the petals; 

 superior sessile ovary, 2-5-celled, with 5 very short styles and obtuse 

 stigmas; one ovule in each cell. Fruit drupaceous. Seeds without 

 albumen. The plants of this order are trees without spines, having 

 alternate unequally piunate leaves without pellucid dots. The flowers 

 are arranged in panicles or racemes. This order was formerly included 

 in Terebinihacea, but has been separated by Kunth and Lindley, on 

 account of their syncarpous fruit and the absence of a resinous juice. 

 The real affinity of Spondiacae appears to be with Aurantiacete, from 

 which they <liff~r in little beyond their perigynous stamens and the 

 absence of dots on their leaves. They are natives of the West Indies, 

 the Society Islands, and the Isle of Bourbon. The fruit of some of 

 the species of Spondiaceie is eatable, and is known in the West Indies 

 by the name of Hog-Plums. 

 SPONDYLID^E. [PECTIWEJE.] 



SPONDY'LUS. [PKCTINID.E.] 



SI'UXOA'RIUM, a genus of Silurian Fossils. 



SPO'NGIA, the geueric name under which Linnceus and many 

 subsequent systematiats have ranked the very numerous forms of 

 organisation analogous to the sponges of commerce. Generally, and 

 we tl.ink justly, zoologists have claimed these organisations for the 

 animal kingdom, and ranked them among the Zoophyta; but there 

 are eminent writers who dissent from this view on different grounds, 

 and prefer to rank the marine and freshwater sponges with plants. 

 For in regard to their constituent structure, they are composed, as 

 o many of the Polypifera are, of a firm horny or stony skeleton, 

 immersed in a soft gelatinous living mass; in respect of the aspect of 

 these two substances, the resemblance which they offer to Altyonia 

 appears very strong, while their external forms, uncommonly varied, 



Spending MoMn. 



a, branch with leaves and fruit; I, flower, showing the hypogynous disc, 

 with the stamens and petals under it ; c, portion of branch, showing inflores- 

 ence ; d, section of fruit, showing its five cells. 



sometimes resemble Alcyonia, often approach to Palmipora, frequently 

 to Pavonia, Agaricia, and other forms of Lamelliferous Zoophyta. 

 The currents of water which pass through the canals of their sub- 

 stance are analogous to many operations among Polypifera and Mol- 

 Imca, and depend on similar ciliary organs, which have been detected 

 in situ in Grantia ciliata. As however they contain no Polypi, it is 

 difficult to rank them under the Polypifera, Dr. Johnson omits, in 

 his excellent work on British Zoophyta, the sponges, and the following 

 summary of his reasons deserves attention: "If they are not the 

 productions of Polypes, the zoologist who retains them in his province 

 must contend that they are individually animals, an opinion to which 

 I cannot assent, seeing that they have no animal structure or indi- 

 vidual organs, and exhibit no one function usually supposed to be 

 characteristic of the animal kingdom. Like vegetables, they are 

 permanently fixed; like vegetables, they are non-irritable; their 

 movements, like those of vegetables, are extrinsical and involuntary ; 

 their nutriment is elaborated in no appropriated digestive sac ; and, 

 like cryptogamous vegetables or alg;c, they usually grow and ramify 

 in forms determined by local circumstances, and if they present ^ome 

 peculiarities in the mode of the imbibition of their food, and in their 

 secretions, yet even in these they evince a nearer affinity to plants 

 than to any animal whatever." On this we may remark, that very 

 many animals are as permanently fixed as sponges ; that irritability 

 is not to be looked for in every part of a sponge, any more than in a 

 Rhizoitoma, whose divided digestive cavities are very unlike ordinary 

 stomachs ; and that the forms of sponges include remarkable analogies 

 with the supports of Polypi. 



It is to our countrymen Ellis and Grant that the history of sponges 

 is most indebted. The former established the existence and nature 

 of the currents of water which pass through the substance ; and the 

 latter, besides confirming the results of Ellis, added a vast quantity 

 of new and valuable observations. Mr. Bowerbank has contributed 



'Microscopical Journal,' 1841.) 



Sponges may be thus characterised : They consist of an albu- 

 minous skeleton and gelatinous matter, forming a mass not irritable, 

 with numerous holes, connected internally with anastomosing canals. 

 The skeleton is either simple, consisting of horny fibres, as the 

 species so commonly used for domestic purposes ; or compound, 

 being strengthened by calcareous or siliceous spicula. Some of the 

 skeletons of sponges are entirely horny ; others are entirely siliceous ; 

 some are entirely calcareous; but the greater number are compound, 

 and consist of horny matter with additions of spicula in various pro- 

 portions. The gelatinous matter, abounding in horny matter and 

 transparent globules, connects the different parts of the skeleton and 

 membranes, lines the various canals, and forms the margins of the 

 openings. The pores are minute openings (on the surface) with a 

 gelatinous margin, strengthened or defended by the skeleton or spieula, 

 into which the water enters in currents, generated probably by a 

 ciliary apparatus, which however has not yet been detected by the 

 microscope, except in Oi-antia ciliata. The water, after trwersing tho 

 interior canals, is ejected by means of orifices which are larger than 



