] 56 Mr. W. S. Kent oti the Emhryology of Sponges. 



Fig. 12. Portion of the cavity of a calcareous sponge (Ascaltis cerebrum, 

 Hkl.), showing at a the internal lining of charactei-istic flagel- 

 late cells, and at 6 a swarm-gemmule in its earlier amoeboid 

 and unsegmented state. (After Haeckel.) 



Fiff. 13. An isolated zooid of Magosphcera planula, Ilkl., derived from 

 the dismemberment of the adult spherical colony form. 



Fig. 14. A similar zooid with the cilia retracted and presenting an 

 amoeboid aspect. 



Figs. 15 &16. The preceding amoeboid zooid, having in the first instance 

 assumed a quiescent or encysted state, and in the second become 

 divided by cleavage into four spherical segment-masses or 

 blastomeres. 



Figs. 17 & 18. Two adult colony-spheres of Magosphcera planula de- 

 veloped in a moruloid manner from a continuation of the 

 cleavage process of the preceding type, the first viewed super- 

 ficially, and the second in optical section. In the latter in- 

 stance the union of the separate zooids with one another by 

 their slender posterior extremities is made manifest, the colony 

 presenting under such conditions a close structural corre- 

 spondence with the swarm-gemmule of the sponge, illustrated 

 by figs. 10 & 11 of the preceding Plate. Both consist of similar 

 unit-aggregations, the separate zooids hi the case of Magosphcera 

 hav-ing numerous terminal cilia, and in that of the sponge- 

 gemmule a single cilium only. (Figs. 13-18 after Haeckel.) 



Fig. 19. A separated sporocyst with spores from a calcareous sponge, 

 Leucosolenia hotryoides, Bow. 



Fig. 20. An intraspicular area of Leucosolenia hotryoides, consisting of a 

 thin film-like expansion of structureless sarcode or syncytium, 

 in which are immersed coUar-bearing sponge-monads in an en- 

 cysted state ; these, as at a, are laden with spores, while, as at 

 b, these spores have been liberated and scattered within the 

 syncytium by the dissolution of the cell-wall of the encysted 

 monads or sporocysts. These liberated spores gradually develop 

 through an amoeboid phase into typical collar-bearing mouads, 

 and fill up the intraspicular loculi, as shown in the succeeding 

 figure. An exceedingly minute triradiate spicule is sho-\vn at 

 sp, developing within the _^substance of the syncytium. X 600 

 diameters. 



Fig. 21. A similar inti-aspicular area of the same sponge, in which the 

 typical collar-bearing monads have increased to such an extent 

 as to completely line it in a continuous pavement-like manner ; 

 the collars of the individual monads, so as not to interfere with 

 the general view, are represented only along the upper margin, 

 and as single instances m the two pores marked p. 



Figs. 22-24. Spore- capsules or sporocysts of a siliceous sponge {Hali- 

 chondria, sp.) derived from the encystment of the ordinary 

 collar-bearing monads. At fig. 24 the sporocyst is bursting 

 and setting free its countless granular spores. 



Fig. 25. Spherical cluster of spore-like bodies from a species of Hyme- 

 niacidon. These are at first enclosed within a membranous 

 sporocyst, and afterwards, falling asunder, become distributed 

 throughout the substance of the syncytium. X 500 diemeters. 



