108 M. E.Hackel on the Organization of Sponges^ 



of all animal 7>%/6r, will be explained more fully in my Mono- 

 graph of the Calcispongise. 



I will admit that this law, which appears to me to be of 

 high importance, is subject to certain modifications in many 

 individual cases, and that perhaps here and there, in both the 

 Sponges and Acalephs, the two germ-lamella? or formative 

 membranes (the entoderm and ectoderm) may replace each 

 other by local substitution. Not unfrequently the entoderm is 

 lost over large spaces, and is replaced by the ectoderm. In 

 some, perhaps in many cases (both in Sponges and Acalephs), 

 the different siimification of the two divergent srerm-lamellge 

 IS, in particular parts of the body, not clearly recognizable, or 

 even actually changed. Thus, for instance, perhaps in both 

 groups of animals, sexual products may sometimes be deve- 

 loped from tlie ectoderm and muscles from the entoderm. But 

 then, probably, these deviations and local substitutions of the 

 two lamella? are to be regarded as secondary modifications^ 

 only produced at a late period hy adaptation. The original 

 primary relation inherited hy all Sponges and Acalephs from 

 the common trunhfbrm (Protascus) is prohahly that described 

 above : the entoderm, as the inner, vegetative germ-lamella, 

 forms the nutrient cells of the canal-epithelium, and the cells 

 produced from these, by division of labour, serving for the pur- 

 pose of reproduction (germ-cells or spores, ova and zoospermia); 

 whilst the ectoderm, as the outer, animal germ-larnella, forms 

 the muscles, nerves, skeletal parts, outer covering, &c. 



This law finds its strongest support in the structure of the 

 young forms of the two groups of animals, which have been 

 already referred to. The cup-shaped young state, produced 

 from the ciliated larva, which possesses a simple stomachal 

 cavity (or digestive body-cavity) with a single, simple aper- 

 ture (or mouth), and which, in the living Prosy cum, still re- 

 calls to us the long-lost picture of the Protascus, shows us its 

 simple solid body-wall (or stomach-wall) composed throughout 

 of the two distinctly differentiated formative membranes, the 

 entoderm and the ectoderm, and, indeed, equally in the corre- 

 sponding young states of the Spongia? as in those of the corals 

 and the Acalephs generally. Here, again, however, the Calci- 

 spongise serve as admirable elucidatory objects, because, on 

 the one hand, of all Sponges they approach nearest to the 

 corals, and, on the other, in the graduated evolution of their 

 simple organization, from the very simple Prosy cum and 

 Olynthus, up to the highly developed Dunstervillia and Cya- 

 thiscus, they bring wonderfully before our eyes the continual 

 separation of the two originally divergent formative mem- 

 branes, the vegetative entoderm and the animal ectoderm, 



