34 Mr. K. G. Harrison on the 



the development of colonies of Hydroida *. Can it be a 

 matter for surprise that the latter, which are doubtless of very 

 small size, have never been seen and may still long remain 

 unnoticed, if we reflect that the statoblasts of which we have 

 been speaking are quite a recent discovery, and, above all, 

 that, in spite of continual watching, it has taken nearly five 

 years to find in London itself, with all the resources of a 

 perfectly equipped laboratory, a hydroid phase of Limno- 

 codium ? t 



IX. — On the Development of the Fins of Teleosts. 

 By Ross Granville Harrison \. 



Excepting the Elasmobranch Fishes, we have no complete 

 knowledge of the development of the extremities of any group 

 of vertebrates. The skeleton alone has received due atten- 

 tion. The muscular system of the limbs of the higher verte- 

 brates has been supposed by recent writers who have touched 

 upon the subject to take its origin from masses of cells 

 derived from the myotomes. These myotomic cells are in a 

 general way to be regarded as homologous with the cells of 

 the muscle-buds (" Muskelknospen ") , out of which the 



* The oyster-beds at certain points of the coast are justly regarded by 

 zoologists as exceptionally rich localities. I have mentioned a very 

 typical example of this lying off Dunkirk. Sponges, Hydroids, various 

 Annelids, Bryozoa, and Cirrhipedes, to speak of fixed animals alone, 

 multiply upon the dead or living shells with singular vigour, and this in 

 spite of* the violence of the gyratory currents, which in these parts may 

 attain a speed of two metres a second (J. de Guerne, " La rade de Dun- 

 kerque," Revue Scientifique, March 11, 1885). 



t A. G. Bourne, " On the Occurrence of a Hydroid Phase of Limno- 

 codium Sowerbi/i, Allman and Bay Lankester," Proc. Boy. Soc. Lond. 

 xxxviii. p. 9. It will be remarked that the basin in Begent's Park in 

 which the Medusse have appeared at intervals, and where the hydroid 

 phase of Limnocodmm has at last been discovered, has been emptied and 

 left dry for a somewhat long period on several occasions. This appears 

 to indicate on the part of this freshwater type a singular power of resist- 

 ance to the most abrupt changes in the condition of the medium. Vide 

 the plate, p. 12 loc. cit. 



While correcting the proofs of the present note I have received no. 1258 

 of 'Nature' (Dec. 7, 1893), containing an article by Prof. Bay Lankester 

 entitled " Beappearance of the Freshwater Medusa (Limnocodium 

 Saivei-byi)." This organism, which had not been observed again in 

 London since July 1890, has unexpectedly come to light at Sheffield in a 

 tank containing aquatic plants sent from Begent's Park. 



X From the ' Johns Hopkins University Circulars,' No. Ill, May 1894, 

 pp. 59-61 : being a preliminary communication. 



