250 Prof. E. Hackel on the Position of the 



Organization of tlie Sponges, &c.," in the following words : — 

 " We should therefore have to divide the stem or phylum of 

 the Zoophytes [Coelenterata s. Zoophytd) into two primary 

 groups (sulphyla or cladi) — 1. Sponges [Sjwngice s. Porifera)^ 

 and 2. Nettle-animals {Acalej^hoi, s. Cnida', s. Nematophora). 

 The latter would divide into the three classes of the Corals, 

 Hydromedusfe, and Ctenophora." But, with reference to the 

 biogenetic fmidamental law and the accordant ontogeny of 

 the Calcispongige and Hydroida [Olynthus and Gordijlophorci)^ 

 we shall have further to extend this view of the immediate 

 relationship of the Sponges and Nettle-animals to the follow- 

 ing proposition : — Sponges and Acalephce are two diverging 

 branches of the Zoophyte stem, lohich have developed themselves 

 from the common stem form of the Protascus, This Protascus 

 is still represented by the transitory young form of the 

 Ascida'^. 



As regards the differences between the Sponges and Aca- 

 lephre, I regard the want of tentacles in the former as quite 

 unessential. They are wanting also in many Acalej^haj (e. g. 

 many Siphonophora and Antipathidce). On the other hand, 

 in some sponges incipient tentacle-formation seems to occur, 

 as, for example, in Osculina polystomella (0. Schmidt, Algier. 

 Spong. 1868, pi. i. figs. 6, 7). What is the condition of the 

 antimer-formation in this and other siliceous sponges requires 

 closer investigation. Certainly the figure which O, Schmidt 

 gives of the fissures surrounding the stomachal cavity in some 

 forms of Osculina reminds one strongly of the Corals ; and his 

 fig. 4, pi. i. (/. c), might actually pass as the transverse section 

 of an octonary Alcyonarian. In other siliceous sponges also 

 the stomachal cavity appears to be divided into compartments 

 by radial septa (of various number) ; and these may be referred 

 to differentiation of antimera. As, however, antimer-formation 

 is wanting to many Hydromedusse, we must not lay too much 

 weight upon this. 



The urticating organs have hitherto appeared to form one 



* The genealogical connexion of tlie Sponges and Acalephre is conse- 

 quently to be sought only down at the root, where, on the one hand, Archi- 

 spoiKjia, the stock form of the Sponges, and on the other Archydrn, the 

 stock form of the AcalephiB, have developed themselves from the common 

 Protascus form ; whereas the near relation of the Sponges to the Corals, 

 to which I formerly gave particular prominence, is to be understood only 

 as an analogy, not an homology. I thought at that time that I found in 

 the radiate structure of the Sycones an essential morphological point of 

 comparison with the Corals ; but the developmental history of the radial 

 tubes of the Sycones, with which I only became acquainted subsequently, 

 has convinced me that these are not homologous with the perigastric 

 radial chambers of the Corals. 



