J. 920] Skeletal Element in Lithistid Sponges 61 



tions from his "Sponges of the Gulf of Mexico" (1879) may be made. 

 ''In the Sponge-fauna of the Atlantic Region, I have shown what a 

 great role within the sponges is played by the phenomenon of conver- 

 gence in the production of pseudo-homologies. These fall- under the 

 general concept of adaptations in so far as one is justified in speaking 

 of adaptations to general mechanical laws" {loc. cit., p. 4). Schmidt 

 goes on to say that his entire criticism of characters, in the work of 

 comparing organisms with one another, aims at distinguishing what is 

 the result of inheritance and what the effect of the environment, the 

 latter "only drawn into the stock of hereditary characters in the 

 course of a gradual process of fixation" (an abstract statement into 

 which more than one meaning may be read). He continues and notes 

 that in most contributions of the time, especially those dealing with 

 embryology, the possibility that morphological agreement is not always 

 based on common descent and heredity, is far too lightly passed over 

 (a habit of mind which the progress of physiological-mechanical 

 studies has greatly changed since Schmidt's time). 

 Chapel Hill, N. 0. 



LITEEATUEE CITED 



Dendy, a. 1905. Eeport on the sponges collected by Prof. Herdman, at Ceylon, 



in 1902. In : Herdman Eep. Pearl Oyster Fisheries, Part III, London. 

 Lendenfeld, E. von. 1903. Das Tierreich, 19 Lieferung. Tetraxonia. Berlin. 



1906. Wissenschaftliche Ergebnisse der deutschen Tiefsee-Expedition, Bd. 



XI. Die Tetraxonia. Jena. 

 Schmidt, O. 1879. Die Spongien des Meerbusen von Mexico (und des Carai- 



bischen Meeres). Erstes Heft. Jena. 

 Sollas, W. J. 1888. Eeport on the Tetractinellida collected by H. M. S. Chal- 

 lenger. Edinburgh. 

 ToPSENT, E. 1897. Spongiaires de la Bale d 'Amboine. Eevue Suisse de zoologie, 



t. IV. 

 Topsent, E. 1904. Spongiaires des Acores. Eesultats des eampagnes scien- 



tifiques accomplies sur son yacht par Albert ler Prince Souverain de Monaco. 



Ease. XXV. Monaco. 

 Wilson, H. V. 1904. Eeports on an exploration off the west coasts of Mexico, 



Central and South America, etc. The Sponges, Memoirs Mus. Comp. Zoology, 



Vol. XXX, 



