MEDUSA OF MICROHYDRA RYDEBI. 641 



the determination of species. The tentacles of Limno- 

 c odium are quite unlike those of Microhydra. I have a 

 few specimens of Limuocodiura which came from Regent's 

 Park in my collection, and they show the tentacles in all 

 stages of development. The tentacles even at their earliest 

 stage, when as mere buds upon the margin of the umbrella, 

 show a character which is not found in the tentacles of 

 Microhydra, nor have I found oryet met with it in any other 

 Medusa. The nematocysts are definitely arranged at the ends 

 of little papillge. At first there are one or two nematocysts 

 in each papilla, but later on the number increases to about 

 five or more. For the purpose of comparison I selected a 

 very small tentacle of Limnocodium, a little over one 

 millimetre in length, and made a drawing (PI. 37, fig. 3) 

 from the central portion of the tentacle to the same scale as 

 the drawing of the tentacle of Microhydra (PI. 37, fig. 2). 

 It will at once be seen that there is a marked difference between 

 the tentacles of these two Medusae. The nematocysts have 

 also a different shape (PI. 37, figs. 4 and 5). 



The Reproduction of Miceohydra. 



The hydroid has two methods of reproduction ; one is 

 asexual, the other is sexual. Mr. Potts considers the 

 budding of new hydranths, which are not set free, to be a 

 second asexual method. The Hydroid is at first a single 

 polyp, later on from its base another polyp is developed, 

 but as the second polyp is not detached a colony of two 

 individuals is formed. The Hydroid phase of Limnocodium 

 in the same manner is also colonial, but has from two to four 

 polyps. This is not a case of reproduction, as there is no 

 increase in the number of independent individuals, but simply 

 one of branching to form a colony. 



The asexual method of reproduction of Microhydra seems 

 to me, from the appearance of the figures given by Potts 

 (PI. 36, figs. 17, 21, 24), to be reproduction by fission, which 

 occurs in certain marine Hydroids. 



