PORIFERA. 799 



Many sponges have been found unisexual, others hermaphrodite, 

 e. g. Sycandra (Sycott) raphanus, Aplysilla violacea, Dendrilla ; others some- 

 times in one, sometimes in the other condition, e.g. Oscarella lobularis, 

 Halisarca Dujardini^. The male element in hermaphrodite species usually 

 ripens first. A coloration indicative of sex has been observed in Chalinula 

 fertilis by Keller though not by Vosmaer, and the male and female Spon- 

 gilla lacustris are said to differ structurally by Marshall. The sexual cells 

 are wandering mesoglaeal cells which ripen in the mesoglaea. The spermato- 

 spore of the Calcarea and Verongia (Aplysinidae) 2 becomes binucleate : its 

 protoplasm so divides that one portion becomes a covering or enveloping 

 cell, whilst the nucleus of the other multiplies and the nucleated mass gives 

 origin to the spermatozoa. The whole spermatospore in other sponges 

 divides into spermatoblasts. The ovum of the Calcarea remains during 

 growth an amoeboid wandering cell, but in other sponges it becomes 

 spherical and acquires a fixed outline. Both spermatospore and ovum 

 in the Non-Calcarea are invested by a capsule of flat epithelium derived 

 from mesoglaeal cells and generally arranged in a single layer, but in 

 Aplysilla molacea and Dendrilla in several layers. And in the two ex- 

 ceptions named both sexual products collect in small masses, each mass 

 invested by a common epithelial capsule with processes separating the 

 individual spermatospores or ova one from another 3 . The ripe ovum 

 is naked 4 , more or less granular, with a clear exoplasm, sometimes pig- 

 mented. It undergoes impregnation, segmentation, and development into 

 a ciliated embryo in situ, except in the burrowing sponge Clione, where 

 it is expelled as soon as it is ripe enough to undergo development 

 (Nassonow). Segmentation is total and as a rule regular ; variably but 

 slightly irregular in Oscarella lobularis ; somewhat irregular in Halisarca 



that the filaments in question, to which he gave the name of Spongiophaga communis, were vegetable 

 parasites ; see his paper on 'Parasites of the Spongida,' A. N. H. (5), ii. p. 165. 



1 The male or female element predominates in a given specimen of Sycandra raphanus. Uni- 

 sexual individuals of Oscarella, &c., may have shed one or the other element. It is possible that all 

 sponges may produce at one time sperm, at another ova. The sexual products ripen in the walls of 

 the cones in Syconidae, among the ampullae of other sponges, in the base of incrusting sponges, or 

 in the endogastric septa, e. g. in Oscarella. 



a Polejaeff, Keratosa, op. cit. p. 72. In the Calcarean Asconidae the ripe sperm-balls may 

 frequently be found projecting into the gastric cavity. Hence Haeckel thought they were derived 

 from endoderm cells. See Polejaeff, Calcarea, op. cit. p. 33, and Vosmaer, Porifera, p. 413. 



3 In A. violacea the number of ova in each mass appears to increase by fission (?) to about forty, 

 and subsequently to dwindle to four. The ovum of the same sponge is separated by a space from 

 the walls of its capsule to which, however, it is suspended by a single peduncle cell. The contents 

 of each mass of capsules ripen simultaneously in Aplysilla but not in Dendrilla. The ova of 

 Euspongia are aggregated 10-30 in number within a small area near an exhalent canal, and the 

 mesoglaea in which they lie is surrounded by a richly anastomosing network of canals. Polejaeff 

 states that the epithelial cells of the capsule of an ovum grow in volume during the formation of 

 the embryo {Keratosa, op. cit. pp. 52-3). 



4 There is an egg membrane in A. molacea (von Lendenfeld), and a calcareous shell in Sycaltis 

 {Amphoriscus} testipara and S. (A^) ovipara (Haeckel, Kalkschwamme, i. p. 157)' 



