Calcispongise in the Animal Kingdom. 257 



to call its aperture not a buccal orifice, but a lyorus ah- 

 dominalis. 



In the case <5f these and of many other difficult morpho- 

 logical conditions, the true and correct conception comes at 

 once in its full power when we consider them in the light of 

 the theory of descent. The first organ which the primordial, 

 multicellular Synamooha must have formed for itself on the 

 commencement of organological differentiation was the in- 

 testine. The inception of nutriment was the first requirement. 

 In this way was produced the Gastrcea, the whole body of 

 which is still intestine, as in the Protascus, and as in Olynthus 

 and Hydra (in the latter leaving out of consideration the 

 tentacles). It was only much later, after the production of 

 the middle germ-lamella, tliat the true body-cavity was formed 

 in the latter (by the splitting of the mesoderm, the solid cell- 

 mass between exoderm and entoderm). In it fluid accumu- 

 lated — the first hlood. In all animals which have a true 

 body-cavity this is filled either with blood or lymph (there- 

 fore communicating directly with the blood- vascular system !), 

 but never with chyme or chyle, or with crude nutritive 

 material. Consequently the cavities of the gastro-canal system 

 in the Sponges and Acalephoe are 7iot body-cavities ^ but an 

 intestinal cavity. 



7. The Origin of the Mesoderm and of the Generative Organs. 



In connexion with the preceding theory of the homology of 

 the germ-lamellje in the whole animal kingdom, some ques- 

 tions closely related to it may be briefly treated. For this 

 jjurpose we assume the alleged homology as proved so far as 

 that the primitive intestine in all animal-stocks, from the 

 Sponges to the Vertebrata, is originally identical, and produced 

 from the entoderm of the Gastrula^ and in the same way the 

 dermal lamella (neuro-corneous lamella) is produced from the 

 exoderm of the Gastrida'^ . 



In the Sponges, certainly at least in the Calcispongiaj and 

 in many other low sponges, the two germ-lamellte persist 

 through life in their original simplicity. In the lowest Acalephse 

 also we still find them so. But even in Hydra a third lamella, 



* The opinion expressed by Kowalevsky {I.e. 1871, p. 6), that the 

 intestino-glandular lamella of the insects is not homologous with that of 

 other animals, but a perfectly distinct lamella, I regard as erroneous. It 

 is precisely among the insects that the ontogeny is very strongly falsified 

 by secondary adaptation. On the other hand, I regard the embrj'onal 

 envelopes (and especially the amnion) as decidedly not homologous in 

 Insects and Vertebrata. They are only analogous envelopes, and are 

 wanting in the lower Vertebrata. 



Ann. & Mag. N. Hist. Ser. 4. Vol. xi. 17 



