September 16, 1898.] 



SCIENCE. 



357 



this CcBlenterate theory on a sound basis 

 by his work on the larvse, which he de- 

 scribed as formed of two layers, an ectoderm 

 and an endoderm. The Coelenterate theory, 

 as modified by the beautiful researches of 

 the Chairman, soon became dominant. It 

 was based on architectural considerations, 

 which rendered the reference of the sponges 

 to the Protozoa impossible. But it did not 

 equally disprove the descent of the sponges 

 from that group. Hence two further rival 

 views had been advanced : (1) that the 

 sponges, though Metazoa, are not Coelen- 

 terata; (2) that the sponges are not Met- 

 azoa at all, but have been developed inde- 

 pendently. The speaker summarized his 

 own researches on the development of the 

 Ascone sponge, Clatharina blanoa, and con- 

 cluded that the evidence appeared to favor 

 the independent descent of the sponges 

 from the Choanoflagellata. 



The general discussion was begun by 

 Professor Haeckel, who summarized the 

 historical progress of opinion. He still 

 clung to the Ccelenterate theory, because 

 he thought that the remarkable resem- 

 blance between the blastula stages of 

 sponges and of admitted Metazoa, such as 

 some mollusca and amphioxus, proved that 

 the whole metazoan phylum was monophy- 

 letic in origin. Dr. Vosmaer, of Utrecht, 

 rather regretted that he had been invited 

 to join in the discussion, because it was 

 very unpleasant for a specialist on a group 

 to be forced into a confession of ignorance 

 regarding it. All he could say was that 

 they did not know the exact position of the 

 sponges in the animal kingdom. Mr. Sa- 

 vile Kent read a statement arguing that 

 the sponges must be the descendants of the 

 Choanoflagellata, as the collared cells of 

 the two groups wei-e known in no other 

 animals and agreed so precisely that they 

 must be homologous. He sketched cases 

 in which Choanoflagellata occurred as ag- 

 gregates of collared cells resting on cells 



without the flagella, and thus reproducing 

 the typical structure of the walls of a 

 sponge blastula. He urged that workers on 

 the sponges should acquire some personal 

 acquaintance with the Choanoflagellata. 

 Professor Schulze closed the discussion by 

 a few general remarks, in which he upheld 

 the Ccelenterate view of the sponge affini- 

 ties. He said all Metazoa could be divided 

 into two sets, those with the elements ar- 

 ranged radially and those in which they 

 were bilateral. He regarded the sponges 

 as members of the former division. 



On the third day a discussion on the ori- 

 gin of the mammalia was opened by Profes- 

 sor Seeley, who began by remarking that 30 

 years ago birds and reptiles were united 

 together owing to the discovery of many 

 features in the skeletons of some fossil rep- 

 tiles, previously known only in birds. But 

 since then many reptiles have been dis- 

 covered of which the skeletons show charac- 

 teristic mammalian features. Accordingly 

 the anomodont reptiles of South Africa and 

 Texas have been united with the mammals 

 as the group Theropsida. The distinctions, 

 based on living reptiles and mammals, on 

 which the separation of the two classes was 

 founded, break down when applied to the 

 fossils. Professor Seeley compared the 

 skeleton of the anomodonts with that of the 

 mammals, and showed, element by element, 

 that there is a remarkable series of resem- 

 blances in structure between them. Thus 

 the specialization of the teeth into canines, 

 incisors and molars, once regarded as 

 characteristic of mammals, occurs also 

 among reptiles ; and in the genus Diademo- 

 don there is a beauty of differentiation 

 which can be paralleled only by the molars 

 of insectivores. Similarly with the limbs, 

 that of Theriodesmus was thought to prove 

 that animal to be a mammal, but it is now 

 known to be a reptile ; and all through the 

 limbs of the anomodonts there runs a strong 

 mammalian strain. The marsupial bones 



