Hyatt] 134 [March 5, 



as their forms and general structure, and that from all points of 

 view they exhibit no traces of derivation from any higher source 

 than the colonial Protozoa. Yon Lendenfeld, though claiming 

 the sponges as properly belonging to the Coelenterata, entertains 

 a similar opinion. "The question whether the sponges digest 

 with the Ectoderm or with the Entoderm cannot yet be decided. 

 But it does not appear improbable that both layers (Polaejeff, I. 

 c.) may have that function. The Keimblatter of other Coelen- 

 terata are nearly analogous, so that we can conclude that the lay- 

 ers of the much less highly organized Sponges are still more so, 

 and that we have in the Sponges different germinal layers before 

 us." (Proc. Linn. Soc. K S. Wales, vol. 9, pt. 2, p. 438.) The 

 opinion of those of us who held that the tissues of sponges were 

 more primitive than in other types of Metazoa was founded 

 largely upon the observations of the structure of adults and their 

 general morphology. It is, therefore, very satisfactory when such 

 a profound student of embryology and histology as Metschnikoff 

 is found to be advocating a similar opinion after minute, thor- 

 ough, and extended investigation of the embryology and histol- 

 ogy of the same forms. In speaking of the general relations of 

 sj^onges to Coelenterata (Zeitschr. Wissen. Zool., 1879, p. 379) 

 this author writes : " Es kann aber nicht bezweifelt werden, dass 

 trotz aller Analogien, die S]Jongien einen viel niederen Zweig der 

 Metazoa als ihre nachsten Verwandten, die echten Coelentera- 

 ten, reprasentiren ; " and farther (p. 377), in describing the rela- 

 tions of the tissues he adds: "dass bei den Schwammen diese 

 Schichten (ectoderm, mesoderm and endoclerm) noch nicht den 

 Grad der Selbstandigkeit und TJnabhangigkeit erlangt haben, 

 welcher bei den holier stehenden Thieren so characteristisch ist." 

 It is not at all adverse to this opinion that intracellular digestion 

 should take place locally in the higher forms of Metazoa. On the 

 contrary it would be very surprising if the cells of the tissues 

 should retain the forms and structures of Protozoa without 

 exhibiting similarity of functions. 1 



The essay of Mr. Saville Kent (Embryol. Sponges, Ann. Mag. 



1 We know from the researches of Metschnikoff (Zool. Anzeig., 1878 and 1880) that 

 intracellular digestion takes place in the Planarians, Hydroids, and Medusae. Parker, 

 (Proc. Roy. Soc, 1880) has also witnessed the same phenomena in the digestive cavity 

 of Hydra, and Lankester (Jour. Micr. Sci., 1881) in the curious Medusa, Limnocodium. 



