244 Prof. E. Hack el on the Position of the 



the primitive Ascon form, Olynthus. This skeletoiiless stock 

 form actually realizes " the scheme of the sponges in the 

 simplest manner," and is to be regarded as the original stock 

 form, not only of the Halisarcina^, but also of all other 

 sponges ; it is the Archispongia of our monophyletic genea- 

 logical tree. 



This Archispongia^ the common stock form of all sponges, 

 is a simple thin-walled sac of a cylindrical, ellipsoidal, or 

 rounded elongate form, a uniaxial, unsegmented person, which 

 is attached by one (the aboral) pole of the longitudinal axis, 

 and at the other (the oral) pole opens by an orifice {osculum). 

 The thin wall of the sacciform body consists of two lamellas 

 or leaves. The outer or dermal laiimia (the exoderm) is 

 composed of a simple layer of non-vibratile cells (which have 

 either remained independent or coalesced into a syncytium) ; 

 the inner or gastral lamina (the entoderm) consists of a simple 

 layer of vibratile flagellate cells, of which, at the attainment 

 of sexual maturity, some are converted into sperm-cells and 

 others into ovi-cells. The thin body-wall is from time to time 

 traversed by unstable simple holes or pores ; and then water 

 enters through these pores into the cavity of the sac (the 

 stomachal cavity), and escapes again from the mouth -oriflce 

 in consequence of the movement of the flagella*. 



2. The Spongice and the Protozoa. 



The wearisome disputes as to the position of the Sponges in 

 the animal kingdom, which have continued even till the 

 present day, ought to be finally settled by the morphology of 

 the Calcispongige. Every zoologist who recognizes develop- 

 mental history as the "true light-bearer" of systematic zoology, 

 must admit that by the ontogeny of Olynthus the very near 

 relationship of the Ascontes and the Hydroida is proved. But 

 before I enter into further details upon this subject, I must 

 say a few words upon the supposed relationship of the Sponges 

 and Protozoa which lias hitherto been accepted by most 

 zoologists t- 



* Whether the simplest sponge-forms, corresponding with the picttu's 

 of Archisponiiia, still exist is not known. Possibly a very near ally is the 

 singular sponge which Bowerbank has desciibed as HuUphysema Tuma- 

 noiviczii (Brit. Spong. vol. ii. p. 76, hg. 359), and which Carter regards as 

 a Polythalamian (Squamniiiliiia). I suspect, on the contrary, that it is a 

 veiy simple Myxospongia, which, like Dysidea, forms for itself a slveleton 

 of foreign bodies (spicules of other sponges, spines of Echinoderms, &c.), 

 but in other respects has the simple structure of Olynthus. 



t The multifarious older opinions as to the position of the Sponges in 

 the system of the animal kingdom are brought together in .Johnston's 

 ' History of British Sponges ' (1842, pp. 2.3-75, history of discoveries as 



