EXPLANATION OF PLATE X. (conliniuJ). 



Fig. 

 16-18. Vol. i. p. 173. Sporocysts of a species ol HalicJiondria, that at Fig. iS burst 

 and discharging minute granular spores, x 600. 



19. ASCETT.A. PRiMORDlALis, Hkl. — Three uniflagellate spores, or so-called sperma- ,.. 

 tozoa, as figured by Ernst Haeckel, x 1600. 

 20-30. Proterospongia H-«CKELI, S. K., vol. i. p. 363— A collared monad which .,■ < 



excretes and socially inhabits a common gelatinous matrix or "zoocytium" 

 resembling the cytoblastema of an ordinary sponge ; 20, a social colony of 

 about forty monads, x Soo ; at « (Z, zooids which, withdrawing their collars 

 and flageUa, have assumed an aspect corresponding with the amoebiform 

 cytoblasts of a sponge-body ; b b, examples with collars and flagella retracted, 

 dividing by transverse fission ; c c, normal zooids, with their collars con- 

 tracted ; .f, spore-mass ; e 2, hyahne mucilaginous zoocytium; 21, smaller 

 colony of eleven zooids only, those aX aaa exhibiting an amoebiform aspect 

 and in one instance extending slender pseudopodia ; 22, small social colony 

 including at a four spore-like bodies produced by the subdivision of a 

 metamorphosed collared zooid, and zX b b two minute, monadiform germs ; 

 23, small symmetrical colony-stock of sixteen zooids, derived from the even 

 and continued segmentation of a single primary unit ; 24 and 25, still younger 

 colonies of two and four zooids only ; 26, solitary attached monadiform germ, 

 having as yet developed neither a collar nor investing zoocytium, x 1000 ; 

 27, more advanced phase of the same zooid, having a well-developed collar 

 and mucilaginous investing sheath, and corresponding at this stage with the 

 earlier phases of Salpingo:ca ampulla, S. K., represented at Plate III. 

 Figs. 19 and 20; 28, metamorphosed collared zooid, projecting a lobose 

 extension of its anterior border beyond the margin of the zoocytium ; 29, 

 spore-mass, as at 21 s, x 1000; 30, social colony viewed in longitudinal 

 optical section. 



