M. E. Iliickcl on the Onjanizntion of Sponges. 107 



"vvith o1j1oii;^-j distant, indistinct j)nnctnres, the intervals very 

 minutely punctured ; body beneath and legs black, glabrous, 

 shining ; antennaj black, slightly thicker outwards. Length 

 4^-5 lines. 



XIII. — On the Organization of Sponges, and their Relationship 

 to the Corals, By Eli^ST HacKEL. 



[Continued from p. 13.] 



What raises our deduction as to the common origin and 

 genealogical relationshi]) of the s])onges and corals to a per- 

 fect certainty is the hitherto entirely overlooked fundamental 

 agreement of the sponges and corals {and, indeed, of all the 

 Ccelenterata) in the ontogenetic huilding-up of their body from 

 two different layers of cells or germ-lamello' — the entoderm and 

 ectoderm. In all Sjwnges (just as in all Acalephs, Corals, 

 Hydromedusai, and Ctenophora) all the parts of the body are 

 developed by the differentiation of two distinct cellular layers 

 — an inner formative membrane, the entoderm, and an outer 

 formative membrane, the ectoderm. In all Sponges, as in all 

 Acalephs, the inner germ-lamella {or entoderm) forms the 

 epithelial lining of the nutrient canal-system, as well as the 

 sjjores or sexual products (ova and zoospermia), which are 

 nothing more than sexually differentiated cells of this canal- 

 e]»ithelium ; the outer germ-lamella (or ectoderm), on the 

 other hand, forms the entire external wall of the canal-system 

 and the principal mass of the body in general, which is 

 differentiated in the higher Sponges and Acalephs into epi- 

 dermis, connective tissue, skeletal parts, muscles, &c. 27ie 

 cells produced from the entoderm or inner formative membrane 

 perform the vegetative functions of nutrition and reproduction 

 both in the Sponges and in the Acalephs. The cells which 

 originate from the ectoderm or outer formative membrane, on 

 the other hand, perform the animal functions of movement and 

 sensation, and serve also as a protective covering and as sup- 

 porting skeletal ptarts for the whole body. It will therefore 

 seem to be not inappropriate if in all Ccelenterata (i. e. in all 

 Sponges and Acalephs) we designate the entoderm (or inner 

 formative cell-layer) as the vegetative germ-lamella, and the 

 ectoderm (or outer formative cell-layer) as the animal germ- 

 lamella. The wide view which is presented to us by this 

 conception, and by its comparison with the coiTcsponding 

 relations of the germ-lamella? in the higher animals, and which 

 is well adapted to elucidate the primitive relationship of all 

 the stems of the animal kingdom, i. e. the common derivation 



8* 



