and their JielafwnsJa'j) to the Corals. 119 



kluclio's Guancha blanca and ray Hijcometra compressa : tliese 

 two calcareous sponges occun*ing in such various forms that 

 they seem to belong sometimes to one and sometimes to anotlier 

 systematic group, and place systematists in the greatest <liffi- 

 cultv. In the following Prodromus of a system of the Calci- 

 spongia^* I have Leen able to get over tliis difhculty only by 

 founchng for them a special order — tliat of the Metrosyca. 



Guancha blanca (from the Canary Islands), in its most deve- 

 loped foiTO, appears as a sponge-stock which bears on one and 

 the same cormus the mature forms of not fewer than four per- 

 fectly different genera^ namely, Oli/nthus among the Monosyca 

 (form A of Miklucho), Leucosolenia (form B) and Tarrns 

 (form D) among the Polysyca, and Nardoa among the Cano- 

 syca (Miklucho's form C). In the same way, the most deve- 

 loped form of the Norwegian Sycometra compressa appears as 

 a sponge-stock ichich hears on one and the same cormus the ma- 

 ture forms even of eight different genera, namely : — Sycarium 

 and Artynas, o{ the family Sycaridic ; Sycidium and Arty- 

 mum, of the family Sycodendrid» ; Sycocysfis and Artynelln, 

 of the order Clistosyca ; and SycojdtyUum and Arty nophyll urn, 

 of the order Cophosyca. But we must regard all these forms 

 united upon one stock as generically different, and not as mere 

 developmental stages of one species, inasmuch as each of them 

 is capable of reproduction, and bears about it in its developed 

 spores the convincing testimony of perfect maturity. In these 

 extremely remarkable and important sjwnges the organic species 

 is to he observed as it icere " in statu nascenti.'"' 



The same is probably true of Sycarium rhopalodes from 

 Norway and Ute utriculus from Greenland, the latter described 

 by Oscar Schmidt, provided that the different forms of these 

 which I have ranged under the genera Sycarium, Artynas, 

 Sycocystis, and Artynella really manifest their specific matu- 

 rity by the possession of developed spores. 



If we retuiTi, in conclusion, to the relation between the 

 sponges and corals, and endeavour to establish artifcicdly the 

 boundary between these two classes of animals, we find no- 

 thing essential except the higher degree of histological dif- 

 ferentiation in the corals, and especially their possession of 

 urticating cells. No sponge forms urticating organs in the cells 

 of its ectoderm, ichilst these are present to a greater or less ex- 

 tent in all Acalepjhs (in all Corals, Hydromedusa>, and Cteno- 

 phora without exception). It must be admitted that tliis his- 

 tological character is in itself very unimportant, and, in respect 

 of both its physiological and its moi-phological significance, is 

 but little adapted for the establishment of a shai-p boundary 

 * A translation of this will appear in our next Number. 



