PROCEEDINGS OF THE SOCIETY. 
287 
correct not only with oil, but also with monobromido of naphthaline. 
To neutralize the over-correction introduced by the monobromide it was 
necessary to close the systems and shorten the tube to about 155 mm. 
to 160 mm. The result is an increase of aperture to N.A. 1-56 with 
manifest improvement of the image, and incidentally also a partial 
obliteration of the secondary spectrum. 
I have further found that a number of American oil-immersions will 
behave in a similar manner. 
To obtain the best results, it is important to provide efficient substage 
illumination. For this purpose I have at command nothing better than 
an Abbe, making either oil or monobromide contact with the slide. 
Doubtless a P. and L. achromatic N.A. 1*40 would be much better. 5 ’ 
Mr. J. G. Grenfell exhibited and described specimens of the Dicyemida, 
which are parasites on the renal organs of Octopus sepia and other 
Cephalopods. Their structure is very remarkable, as they consist of a 
long central cell, in which the complicated reproductive processes take 
place, and a few nucleated cells loosely attached to this. There is thus 
no central body-cavity. Hence their discoverer, E. van Beneden, who 
has just been made an honorary Fellow of the Society, claimed for them 
a position on a par with the Protozoa and Metazoa, calling them the 
Mesozoa. But they are generally regarded as Metazoa altered and 
degraded by parasitism. They are not to be found in our museums or 
private collections, and very few persons have ever seen them. One of 
the principal reasons for this, apart from the difficulty of getting live 
Cephalopods, is the fact that when killed by the ordinary reagents they 
break up into their constituent cells. He had, however, succeeded in 
getting over this difficulty by hanging bits of the kidney by threads 
beneath the surface of sea-water in a tumbler, and then adding enough 
chromic acid solution to give a very pale colour. Under these circum- 
stances the Dicyemida left their hold on the kidney and fell to the 
bottom without disintegration, and died there. They could then be 
transferred to the ordinary preservative reagents. The method has the 
further advantage of obtaining the specimens free, or nearly so, from 
the mass of disintegrated kidney-cells which always accompany the 
Dicyemida when a bit of kidney is teased on a slide. 
Mr. Grenfell illustrated the subject by drawings upon the board. 
The President said this creature was certainly a very remarkable 
one. The communication had been very clearly put, and had been" a 
most interesting one. 
Mr. T. C. White having taken the chair, 
The President read a paper on the Uropodinae , which he explained 
might be considered as in continuation of some papers read in 1889 and 
1890, on the Anatomy of the Oribatidae. He had then purposed doing 
the same thing in regard to the Gamasinae , but had been struck with the 
anatomy of these Uropodinae , and had given some attention to them. 
Mr. T. C. White said they knew very well that whatever their 
President touched was sure to be dealt with most lucidly, and his com- 
