Mr. W. S. Kent on the Emh-yology of Sponges. 153 



monads or Spongozoa by the means of spores represents the 

 constant and normal manner in which the growth and exten- 

 sion of the sponge-colony is effected — the aggregated masses 

 of individuals or swarm-gemmules, liberated only at certain 

 periods, representing a special development for the more 

 extensive dissemination of the species. The subject of spore- 

 formation, associated with the reproduction of sponges, has 

 been already adverted to in my contribution to the ' Annals ' 

 in January last, and is entered into at considerable length in 

 my communication made in June 1877 to the Linnean Society. 

 Pending the publication of these more abundant details, 

 figs. 19 to 25 of Plate VII. accompanying this article will 

 assist to illustrate some of the more conspicuous phenomena 

 that accompany this method of reproduction. 



I gladly avail myself of the present opportunity of recording 

 my most grateful acknowledgments to the Government-Grant 

 Committee of the Royal Society, who, by their liberal award 

 to me of a grant of £50, have placed at my disposal those 

 instruments of precision not otherwise accessible, but absolutely 

 requisite for the accurate determination of the ultimate struc- 

 ture and affinities of the group of organisms discussed in this 

 communication. 



Channel-Islands Zoological Station, 

 St. Hellers, Jersey, June 21, 1878. 



EXPLANATION OF THE PLATES. 

 Plate VI. 



Fig. 1. Typical spongozoon or coUar-bearing monad of the calcareous 

 sponge-form Grantia compressa, X 1000 diameters, n, endoplast ; 

 c.v, contractile vesicle. 



Fig. 2. The Amaba-like body from the same sponge-form, out of which 

 by segmentation the swarm-gemmule or so-called ciliated embiyo 

 is produced — which may represent either a typical sponge- 

 monad, as at fig. 1, that has withdrawn its collar and flagellum, 

 and assumed an amoeboid phase, or a similar monad in its unde- 

 veloped and cytoblastic state. 



Figs. 3-8. Successive developmental phases of the swarm-gemmule of the 

 same sponge, commencing with the assumption by the last- 

 named amoeboid body of a spheroidal form, and terminating in 

 the production of a morula-like aggregation of segment-massea 

 or blastomeres. 



Figs. 9, 10. The characteristic form of the swarm-gemmule when libera- 

 ted from the syncytium of the parent sponge, viewed at fig. 9 

 superficially and at fig. 10 in optical section ; the segment-masses 

 of the preceding morida-like body have assumed a conical shape, 

 radiating from the centre to the periphery, each of the same 

 ' bearing in the centre of its exposed or distal border a single 



cilium or flagellum. X 350 diameters. 



