HAECKEl's recent additions to GASTRiEA-THEORY. 65 



doderm and ectoderm. Haeckel fell into pardonable error as 

 to the mode of formation of this Gastrula of the Calcispongise. 

 MetschnikofF, following him, had got an inkling of the true 

 mode of formation^ namely, that there was a process of inva- 

 gation taking place in a blastosphere or one-cell-layered sac, 

 but his observations were most incomplete, and his reason- 

 ing from them so much influenced by animus against 

 Haeckel, that he has given the most erroneous account 

 of the matter, which has been published. Oscar Schmidt 

 failed to interpret correctly what he saw. The truth is that 

 the Gastrula of the Calcareous Sponges, or at any rate of the 

 species which all these observers have more especially studied, 

 namely, Sycandra raphanus, is formed on the amphiblastic 

 type. Oscar Schmidt saw the Amphiblastula (fig. 19), as did 

 also MetschnikofF, but strangely enough, Oscar Schmidt 

 failed to trace the invagination of this Amphiblastula to 

 form the Amphigastrula (fig. 18), as he should have done. 

 Consequently he mistook the whole process, declared that 

 the Sponges had no gastrula-form at all, and concluded 

 that all Haeckel's " schonen theoretischen Folgerungen " 

 drawn from the fundamental fact of the Sponges possessing 

 a Gastrula, must be abandoned. 



Oscar Schmidt must have said this with some pain, for he 

 has proved himself a very fair and well-disposed critic of 

 the Gastrsea-theory. He will therefore probably be well 

 pleased that Franz Eilhard Schulze, working at Trieste, has 

 made most complete observations on the e^^ of Sycandra 

 raphanus and its development to the gastrula-form, and 

 published them in the ' Zeitschr. fur Wissensch. Zoologie,' 

 Bd. XXV, Supplement. Schulze has followed with absolute 

 precision the cleavage-formation of an Amphimorula, of an 

 Amphiblastula, and, by invagination of the large non-ciliated 

 granular cells of the last, of an Amphigastrula in Sycandra 

 raphanus. His drawings are executed with the greatest 

 care and are obviously ' nature-true.' Thus the attacks upon 

 the germ-layer- or Gastrula- theory from the point of view of 

 the Calcareous Sponges are definitely put an end to. Haeckel 

 holds, as is clearly very probable, that the Archiblastic type 

 also occurs among Sponges, and it is possible enough that 

 the Periblastic type also presents itself. 



NEW SER. VOL. XVI. 



