28 Dr. Reid on the Development of the Medusa?. 



these animals *, where he describes four canals, — one in each 

 an^le of the extensible membrane surrounding the mouth and 

 forming the lips, — passing from the circular canal already men- 

 tioned, and also another circular canal placed in the free margin 

 of the lips, I repeated my examinations ; and though I used 

 glasses of very different magnifying powers, and made numerous 

 trials, I could not satisfy myself of the existence of these canals. 

 No doubt four equidistant white lines presenting the appearance 

 of canals are seen, in certain conditions of the extensible lips, 

 running in the positions indicated by Stcenstrup ; but in some of 

 the numerous forms which the lips assume these lines entirely 

 disappear, and when present they seem to be formed by narrow 

 ridges on the external surface, resulting from the quadrangular 

 shape assumed by the lips. The free margin of the lips fre- 

 quently presented indications of the presence of a canal, but I 

 could never satisfy myself of its actual existence. In making 

 such investigations, it must be kept in mind, that the internal is 

 readily separated by pressure from the external layer, otherwise 

 we may be led into error. In the almost daily examinations I 

 have made of these animals during the last two years, I never 

 observed the slightest traces of the hollow quadrangular body 

 described by Steenstrup as growing from the lower surface of 

 the cavity or stomach in the body of the animal, sometimes pro- 

 jecting as high as the mouth, and placed in the middle of the 

 stomach, like the clapper in a bell. 



The inner surface of the lips and of the stomach, and the ex- 

 ternal surface of the tentacula and body, are covered with very fine 

 cilia, so that currents of water, unless when the mouth is shut, 

 are constantly passing in and out from the mouth and along the 

 tentacula. The cilia upon the external surface of the body re- 

 quire the use of the higher object-glasses for their detection, and 

 for a long time they escaped my notice. 



The colony of larva first obtained began to produce buds and 

 stolons about the middle of January 1846, and the other two colo- 

 nies at the end of July of the same year. With intervals of com- 

 parative repose they have gone on reproducing abundantly ever 

 since; so that, notwithstanding they are constantly suffering 

 loss by death and other causes, the number of individuals in 

 each colony has greatly increased. Whenever buds and stolons 

 are formed, they commence by a thickening of the internal layer 

 at those parts, causing a bulging outwards of the external layer. 

 A single bud (fig. 10 a), occasionally two buds, grow from the 

 upper surface of the stolon, and these become developed into 

 larva? in the manner described by Sars. The buds form upon 



* On the Alternations of Generations, &c, translated for the Ray So- 

 ciety, pp. 22, 23. 



