Dr. M. Djbowski on Dosilia Stepanowli. 2-19 



vertebrate upon its back, the problems of fore-and-aft sym- 

 metry, and the question of torsion in the fore and hind limbs 

 of Mammals, have, if we are not mistaken, lost much of their 

 interest and value in the light of modern evolutionary 

 jorobleres, and savour more of scholasticism than of science. 



At all events the present problem is, as embryology shows, 

 so remote in its bearings, — the common point of origin of 

 Arthropod and Vertebrate, the fork in the primitive develop- 

 mental path wliere the two branches began to diverge, is set 

 so far back in the animal scale, and is so remote in geological 

 time, that with our present knowledge we are inclined to 

 regard the consideration of such problems as belonging rather 

 to metaphysics than to pure science, although it should be 

 granted that furtlier researches among the lower worms may 

 yet result in tlie discovery of facts bearing upon the origin of 

 the singular diiferences in the disposition of the arthropod and 

 vertebrate nervous systems. 



In conclusion, therefore, we are led to endorse the fol- 

 lowing opinion of Gegenbaur, in his ' Comparative Anatomy ' 

 (Pjuglish translation) : — " Tlie greater size of the cephalic 

 ganglion compared with that of the ventral ganglia has been 

 already seen in many of the Annulata; in the Arthropoda it 

 is ordinarily still more distinct ; this condition may be partly 

 explained by its relations to the more highly developed organs 

 of sense, if we recognize in the dorsal oesophageal ganglion 

 something similar to the brain of the Vertebrata, Led by an 

 idea of tliis kind, some have compared even the ventral 

 ganglia or ventral medulla with the dorsal medulla of the 

 Vertebrata, and have striven to carry the comparison still 

 further ; these attempts ignore the complete ditference 

 between the type of structure of the Arthropoda and of the 

 Vertebrata" (p. 252). 



XXX. — A Contrihution to tlie Knowledge of tlie Freshwater 

 ISponge Dosilia Stcpanowii. By Dr. M. Dybowski*. 



In the description of the freshwater sponge, Dosilia'^ Ste- 

 panoioiif, recently published by me, I lett its gemmules 

 entirely out of consideration, because none were present in the 



* Translated Toy V\\ S. Dallas, F.L.S., from the' Zoologischer Auzei- 

 gpr,' no. 175, Septeii.ljer 1, 1884, p. 470. 



t l>ybo\vslu, '-Notiz iiber die aus Siid-Eussland stammenden Spon- 

 gillen," in Sitzungsb. d. naturf. Gesellsch. d. Ur.iv. iJorpat, liaud vi. 

 p. 507 (translated in this journal for July 1884, p. 58), and 'Travaux 

 de la Societe des Natuialistes de rULiversite de Chaikow,' vol. xvii. 

 (1883), p. £89, pi. vii. tig. 1 a-d, in Kussian, 



