GENUS PROTOSPONGIA. 363 



separate animalcules ; flagellum attenuate, two or three times the length 

 of the body, conical collar embracing its base for about a distance of one- 

 eighth of its total length ; contractile vesicles two in number, posteriorly 

 situated, endoplast spherical, subcentral. Length of zooids 1-1500", altitude 

 of branching zoocytium 1-60". Hab. — Freshwater. 



Only in the most luxuriant and fully grown examples does the zoocytium of this 

 species present the profusely branched contour delineated at Fig. i of the accom- 

 panying plate, and which, in this instance, may be appropriately compared 

 with the gelatinous polyzoarium of the marine polyzoon Alcyonid'min gelatinosum. 

 As a contrast to this, it frequently exhibits a but slightly elevated lobulate aspect 

 closely approaching that of Spongoniotias uvcila, every phase of gradation occurring 

 between these two extremes. Multiplication in the present type is, according to 

 Stein, effected by transverse fission. Neither this nor the preceding form appear so 

 far to have been discovered in British waters. 



Genus II. PROTOSPONGIA, S.K. 



(Greek, /r^/^j, first; spoggos, sponge.) 



Animalcules normally ovate or pyriform, but more or less plastic and 

 variable in contour, bearing a single terminal flagellum whose base is 

 embraced by a well-developed, extensile and contractile, funnel-shaped 

 collar ; forming extensive colony-stocks, excreting and inhabiting a 

 common mucilaginous matrix or zoocytium, within the substance of which 

 the bodies remain constantly immersed, the collars and flagella only being 

 projected into the surrounding water; endoplast and one or more contractile 

 vesicles usually conspicuous ; increasing by binary fission and by the sub- 

 division of their entire body-mass into sporular elements. 



This new generic group is established for the reception of a single recently 

 discovered Flagellate type which corresponds with Phalansteriiim in so far as that the 

 animalcules excrete, and live more or less completely immersed within, a common 

 mucilaginous matrix or zoocytium. An important distinctive feature is, however, 

 to be noted in the fact that the collar, in place of being rudimentary and having 

 a permanently conical and contracted aspect, attains to its full development, being 

 capable of contraction and expansion, exhibiting circulatory currents, and in all ways 

 corresponding with the normal condition of this structure as existing in the 

 preceding families of the Codonosigidse and Salpingoecidse, and throughout the entire 

 section of the Spongida. 



The importance of the position occupied by the typical representative of this 

 genus with relation to the last-named group, that of the sponges, can scarcely be 

 over-estimated, and is fully explained in its succeeding specific description. With 

 reference to the relationship indicated, this interesting type is herewith dedicated 

 to, and specially commended to the notice of, the illustrious evolutionist of Jena. 



Protospongia Haeckeli, S. K. Pl. X. Figs. 20-30. 



Zooids more or less ovate or pyriform, but exceedingly plastic and 

 variable in shape, from one and a half times to twice as long as broad, 

 sometimes pointed and more attenuate posteriorly, these proportions in 

 other instances being precisely reversed, often assuming an altogether 

 irregular amcebiform contour, the flagella and collars under such conditions 

 being entirely retracted ; collar when fully extended equalling or even 



