TRANSACTIONS OF SECTION D. 789 



8. Report on the Comparative Histology of Cerebral Cor ex. 

 See Reports, p. 453. 



9. Report on the Micro-chemistry of Cells, — See Reports, p 449. 



10, Observations on the Development of the Cetacean Flipp'ir. 

 By Professor JoitNSON Symington. 



11. The Articulations between the Occipital Bone and Atlas and 

 Axis in the Mammalia. By Professor Johnson Symington. 



MONDAY, SEPTEMBER 10. 



The following Papers and Report were read : — 



1. Mnestra parasites, ^/'o/mi. Preliminary Account. 

 By R. T. Gunther, M.A., F.R.G.S., Magdalen College, Oxford. 



During the spring of the present year the prevailing westerly winds no douht 

 contributed to the fact that an unusually large number of P/ii/llirkoe bucephala were 

 ■ captured in the Bay of Naples. I examined every specimen 1 could get hold of 

 and found that of thirty-one individuals of Phyllirhoe taken between March 28 

 and April 20 nineteen, or more than half, had a Mnestra adhering to them. My 

 friend Cavaliere Lo Bianco in the kindest way placed his store of spirit-preserved 

 material at my disposal for examination. Unfortunately the dates of capture 

 ■were not noted, but of forty-three Phyllirhoe every one had or had had a Mnestra 

 upon it. 



From this relative abundance of the parasite it follows that the reproductive 

 power of the Mnestra must be far and away in excess of that of the Phyllirhoe 

 bucephala of the Bay of Naples. Indeed, the fertility of Mnestra must, one would 

 think, be greater than is usual even among parasites. It is therefore most remark- 

 able that hitherto the method of the propagation of Mnestra should have remained 

 undiscovered. We do not know whether it reproduces itself by a sexual or an 

 asexual process, by eggs or budding. 



It was in consequence of our ignorance of this point that systematists have not 

 been able to assign Mnestra to its proper place in the system of Haeckel — which 

 primarily depends upon the place of development of the genital cells in the Medusa. 



I have, however, been fortunate enough to discover other characteristics of the 

 Mnestra which will enable us to unhesitatingly affirm that it should be classed 

 with the Cladonemida, a family of the Anthomedusse. 



The Mnestra is attached to the Phyllirhoe by its manubrium, which is com- 

 paratively short and serves the purpose of obtaining nutriment, apparently by 

 sucking the blood of the host. The shape oi the body of the Mnestra varies greatly. 

 The margin of the umbrella is sometimes notched, but this marginal notch is by 

 no means so constant in its presence as to justify us in regarding it as Claus ' 

 did, a characteristic of Mnestra. The shape of the Medusa can be well described 

 as that of a bun with a large inpushing or * dimple ' in the middle of the exumbral 

 surface, from which, in typical cases, four furrows proceed interradially to the 

 margin. It is by the intensification of one of these grooves that the notch of 

 Claus is often produced. The symmetry of the velum and circular canal is 

 generally not much affected by these furrows on the surface of the ex-umbrella. 



The tentacles are four in number. The majority of specimens examined had 

 two reduced to mere knobs, and some had three or even all the tentacles reduced 

 to this condition. It seemed to me that the reduction of the tentacle was a mark 



' Claus, Verh, Z^ol. Bot. Tr\st., Wign, j,xv, 187?, 



