194 MR. a. J. ROMANES ON MONSTROUS FORMS OF MEDUSA. 



of the effect which we are considering is to be attributed to their 

 influence. And forasmuch as I observed that towards the end of 

 the season the Medusae were of small size, whether or not they 

 were infested by the parasites in question, I conclude that causes 

 other than the one which I previously mentioned must be chiefly 

 concerned in producing this effect. 



DESCEIPTION OF PLATES. 

 Plate XV. 



Fig. 1. Tiarojpsis indicans, n. sp. Natural size. 



2. Thaumantias erucifera, n. sp. Natural size. 



3. Tiaropsis polydiademata, n. sp, Natural size and colour. 



4. Tiaropsis oligoplocama, n. sp. Natural size. 



5. Thaumantias helicobostrycha, n. sp. Natural size. 



6. Diagrammatic representation of the ovaries and nutrient tubes as they 



occur in a normal specimen of Aurelia atcrita. The manubrium, 

 which normally presents four lobes, has been removed. 



7. Diagrammatic representation of a specimen of A. aurita, which pre- 



sented an abnormal, though symmetrical, multiplication of parts — 

 there being twelve complete segments instead of eight (as in fig. 6), 

 and the manubrium, which is not shown, having presented six lobes 

 instead of four. 



8. Diagrammatic representation of an asymmetrical multiplication of parts 



in A. aurita. In this specimen the manubrium was bifid in the lobes 

 which faced one of the multiplied segments. 



9. Diagrammatic representation of an abnormal, though symmetrical, mul- 



tiplication of nutrient tubes in A. aurita — those in every alternate 

 segment having undergone duplication. In this instance the manu - 

 brimn resembled the ovaries in not partaking of the duplication. 



Plate XVI. 



Fig. 1. Diagrammatic representation of a specimen of A. aurita, resembling 

 that figured in Pl. XV. fig. 9, except that one of the four normal 

 quadrants of the umbrella has escaped the process of duplication. 



2. Diagrammatic representation of an asymmetrical multiplication of parts 



n A. aurita, one of the four quadrants of the animal having become 

 duplicated. In this instance, however, the manubrium was four-lobed. 



3. Diagrammatic representation of another form of asymmetrical multipli- 



cation of parts in A. aurita, one of the four quadrants of the animal 

 having become tripled. In this instance the lobe of the manubrimn 

 which faced the tripled quadrant of the umbrella was doubled. 



4. Diagrammatic representation of an abortion of parts in A. aurita, one of 



the four quadrants of the animal having been suppressed. In this in- 

 stance, however, the manubrium presented its normal number of lobes. 

 6. Diagrammatic representation of a still further abortion of parts in A. 

 aurita, two of the fom" quadrants having been suppressed. In thi s 

 instance also, the manubrium presented its normal number of lobes. 



