VAEIETIES, AND MONSTROUS EOEMS OF MEDUSA. 193 



such cases is the strictly symmetrical manner in which the ab- 

 normal developments or abortions are usually found to occur. In 

 most cases these developments, or abortions, extend propor- 

 tionally to all parts of the organism. In other cases this is not 

 so ; and of these cases the most numerous are those in which 

 the ovaries and manubrium are unaffected, while the seg- 

 ments of the umbrella are multiplied. In some cases, on the 

 other hand, a deficiency or absence of the ovaries entails no 

 corresponding deficiency or absence of any of the other organs. 

 Lastly, it may be added that in every case of multiplication of 

 segments which I have ever seen, the supernumerary lithocysts 

 always occurred at the end of a faintly coloured radial tube, and 

 never at the end of a strongly coloured one. Whether the marked 

 difference in the coloration of the two sets of radial tubes implies 

 any corresponding difference in their physiological functions, is a 

 point which I have not been able to ascertain ; but if such is 

 the case, I should be inclined to suspect, from the uniform rule 

 just mentioned, that whatever peculiarity of function it is which 

 renders necessary the high coloration of the radial tubes that 

 alternate with the lithocysts, is a peculiarity which is incompatible 

 with the presence of a lithocyst at the end of the tube. 



Prom the additional observations detailed in this paper, it will 

 be evident that no stress is to be laid on the fact of the most usual 

 form of multiplication of parts in Aurelia being proportionally the 

 same as that which appears to be the most usual form, of multipli- 

 cation in Sarsia (see former paper, p. 529). 



This year, as last year, I observed " that towards the end of 

 August all the individuals of this species (i. e. Aurelia aurita) 

 began to undergo a marked diminution in size." In my previous 

 communication I expressed myself in favour of the view that this 

 progressive diminution in the size of individuals composing 

 the incoming generations of Aurelia was due to the increasing 

 numbers of a parasitical Crustacean {Hyperia galha) ,^^ which ap- 

 peared to devour with avidity all the coloured parts of their hosts." 

 There can, I still think, be little doubt that such parasites, by im- 

 pairing or destroying the nutritive system of these Medusas, must 

 hinder, or entirely stop, the growth of the latter ; but that the 

 small size of Aurelia towards the end of the season is not to be 

 attributed to this cause alone, I have during the present autumn 

 obtained satisfactory evidence. For this year the numbers of 

 Hyperia galba were not nearly so great as they were last 

 year ; so that I am now better able to determine how much 



