6 M. E. Iliickel on the Organization of Sponges^ 



one of the smallest legions of the class of s])ono-eSj and, more- 

 over, for the major part, contains exceptionally small, nay, 

 even microscopic forms, it is nevertheless capable, more than 

 all other sponges, of throwing a valuable general light upon 

 the conditions of organization and alhnity of the whole class. 

 Moreover the sj)ecial systematic and morphological relations 

 of this small order are so simple and clear, and the genealo- 

 gical relationshi])s of its different genera and species so instruc- 

 tive and interesting, that a thorough elucidation of them is 

 of great importance even to the general classification of or- 

 ganisms. 



As the most important result of my investigations, I start 

 with the following general proposition : — The sponges are 

 most nearly allied to the corals of all organisms. Certain 

 sponges differ from certain corals only by a less degree of histo- 

 logical differentiation, and especially by the want of urticating 

 organs. The most essential peculiarity of the organization 

 of sponges is their nutritive canal-system, which is both ho- 

 mologous with and analogous to the so-called coclenteric vas- 

 cular system, or gastrovascular apparatus of the Coclenterata. 

 In the sponges, just as in the corals, and, indeed, in the 

 Coelenterata generally, all the different ])arts of the body 

 originate by differentiation from two primitive simple forma- 

 tive membranes or germ-lamellae, the entoderm and the ecto- 

 derm. These two lamella? originate by differentiation from the 

 originally homogeneous cells which (having been produced by 

 the segmentation of the ovum) compose the sjiherical body of 

 the ciliated embryo or of the i)rimitive larva {Plamila). From 

 the inner or vegetative germ-lamella, the entoderm, originate 

 the nutritive epithelium of the canal-system and the reproduc- 

 tive organs. From the outer or animal germ-lamella, the ec- 

 toderm, all the other parts originate. 



Before I proceed to support this proposition by a brief state- 

 ment of the results of my observations, I may be permitted to 

 make a few remarks upon the position which, in accordance with 

 it, the sponges will henceforward have to occupy in the system of 

 the animal kingdom, beside or below the Coelenterata. For as we 

 must infer, from the general homology which exists between all 

 parts of the sponge- and coral-organisms, not merely an apj^arent 

 anatomical agreement, but an actual blood-relationsliip of the 

 two classes of animals, the rpiestion forces itself upon us, with 

 respect to the system, what particular place the sponges will 

 have to take in the existing classification of the Cfolentcrata. 



In recent zoological systems the stem or type of the Coelen- 

 terata is pretty generally divided into three classes : — 1. Corals 

 (Polypes or Anthozoa) ; 2. Hydromedusa! (Hydroida and 



