VAEIETIES, AND MONSTROUS FOllMS OS MEDUSiE. 191 



only five segments. These, however, were all complete and exactly- 

 equal to one another. 



In the ease of Aurelia aurita deviations from the normal type 

 are of frequent occurrence. It is remarkable, however, as pointed 

 out in my former paper, that such deviations nearly always take 

 place in the direction either of multiplication or of abortion of 

 entire segments. As I have this year paid particular attention to 

 this subject, I will here describe all the more noteworthy forms of 

 variation which I have observed : and to render my description 

 intelligible, it is necessary to begin by describing the normal 



type. 



Fig. 6 (PL XY.) represents Aurelia aurita in full diastole, with its 

 manubrium removed. It will be observed that the organism is con- 

 structed on what we may metaphorically term a very definite plan. 

 The ovaries are four in number, equal in size, and arranged sym- 

 metrically round the centre of the animal. The lithocysts, or 

 ganglia, are eight in number, and are disposed round the margin of 

 the animal at points equidistant from one another. These eight 

 organs thus bear a very precise geometrical relation to the four 

 central organs ; and this relation is, as it were, mapped out by 

 the distribution of the radial tubes. For it may he observed by a 

 glance at the diagram that although most of the nutrient tubes 

 branch and anastomose as they proceed from the centre to the 

 circumference of the umbrella, there is a marked exception to 

 this mode of distribution in the case of some of these tubes — those, 

 namely, which proceed from the centre to the circumference in 

 perfectly straight or radial lines without branching. Moreover, 

 closer inspection will show that these radial or unbranching tubes 

 are disposed with perfect symmetry. For one such tube passes 

 radially to each of the eight marginal ganglia, and each of the 

 eight segments of the circle thus marked out is bisected by ano- 

 ther radial or unbranched tube. There are thus altogether sixteen 

 radial or unbranched tubes, which serve to mark out the whole 

 umbrella into as many equal segments. It must further be ob- 

 served that those straight tubes which proceed to the marginal 

 ganglia differ from those which alternate with them in being less 

 deeply coloured. Lastly, I may add that in the normal type of 

 Aurelia the manubrium (which is not represented in the figures) 

 presents four equal lobes. 



Such being the normal type of Aurelia, the following are the 

 more important deviations from it which I have observed. The 

 most usual is that which I described in my former paper, aad 



