112 



EECEEATIVE SCIENCE. 



tlie wKole fabric togetlier by a felt of 

 spicules. 



The intermediate substance is the seat of 

 the vital forces ; figuratively speaking, it is the 

 heart of the sponge. It consists of circular 

 cells and of spermatozoa in every stage of 

 development. " The cell throws out a long 

 filament, which becomes the tail of the 

 spermatozoon, and becoming longer and 

 pointed, forms, itself, the head. The perfect 

 spermatozoa have long, pointed, somewhat 

 triangular heads, about aoVo^h of an inch in 

 diameter, with truncated bases, from which 

 a very long filiform tail proceeds. The 

 ova are of various sizes ; the largest are 

 oval, and about gioth of an inch in diameter. 

 They have a very distinct vitellary mem- 

 brane, which contains an opaque coarsely gra- 

 nidar yolk." These details are presented 

 at 9, where the ova may be seen embedded 

 amongst the stellate bodies. 



It should be borne in mind that the order 

 of reproduction, so clearly explained by Pro- 

 fessor Huxley, has been seen only in Tethys, 

 and it is therefore only by analogy that we 

 can predicate a similar propagation of ova in 

 sponges generally. Lieberkiihn has observed, 

 in the fresh-water sponges, small moving 

 corpuscles similar to the spermatozoa of 

 Tethys, and to Carter we are indebted for 

 drawings of the seed-like bodies occurring 

 in Sjpongilla meyeni, of which a portion of 

 one is represented at 6. These are a sort of 

 leathery capsules, externally tessellated by 

 spicula, which in section give them the ap- 

 pearance of toothed wheels. The capsule 

 is fiUed with spherical cells containing ova, 

 which when mature escape, through a hilum 

 from the seed-like body, under the form of 

 a gelatinous mass, in which certain changes 

 begin, and the new life of the myriad germs 

 is developed according to the order appointed 

 them. But another mode of propagation is 

 by what Lieberkiihn calls " swarm spores," 

 which are proverbially only the seed-like 

 bodies in a peculiar stage of development. 



Be that as it may, Lieberkiihn obtained 

 swarm spores in active ciliary motion. In a 

 few days they sank to the bottom of the ves- 

 sel, where they began to adhere. They then 

 expanded into a layer of gelatinous substance, 

 and the characteristic flinty needles were pro- 

 duced, and on the twentieth day became bona 

 fide and recognizable sponges. Those who are 

 familiar with the physiology of the protozoa 

 will find no difficulty in reconciling with 

 this distinct spermatozoid reproduction, a sys- 

 tem of increase by gemmules and divisions. 

 Sponges certainly do produce bud-like ofisets 

 which become provided with cilia, and row- 

 ing away from the parent mass, establish 

 themselves elsewhere as new colonies. The 

 lower we descend in the ranks of both animal 

 and vegetable life, the more numerous do we 

 find the provisions for extension of the spe- 

 cies. An Actinia may be cut in twain, and 

 therefrom become two distinct creatures, 

 each capable again of multiplication by ova ; 

 and below this low type, the possibilities of 

 reproduction are still more varied, and evince 

 the abundant provision of the great Archi- 

 tect of the whole scheme for the preserva- 

 tion, against all accidents and chances, of the 

 humblest atoms of organized dust on which 

 he has set the seal of his wisdom and power 

 and infinite goodness. 



In future papers we shall endeavour to 

 indicate the chief points of interest discover- 

 able in the several orders of animal life that 

 abound upon our shores, especially taking 

 note of those which most readily adapt them- 

 selves to the confined area of an aquarium. 

 Those who would follow out into detail the 

 history of the sponges will be best aided 

 by Dr. Gr. Johnston's "History of British 

 Sponges," Griifith and Henfrey's "Micro- 

 graphic Dictionary," and an excellent " Ma- 

 nual of the Protozoa," by J. E. G-reene, 

 B A., in " Galbraith and Haughton's Scien- 

 tific Manuals." 



Shieley Hibbebd. 



