526 TRANSACTIONS OF SECTION D. 
Hyznodontide and Canidz, where, although the evolution had taken place in 
different teeth (the fourth upper premolar in the Canide, the second upper 
molar in the Hyznodontidz), yet the tissues involved were the same in the 
converging groups; but sometimes convergence took place between structures 
formed from quite different tissues, as in the dentition of Thylocoleo and the 
not dissimilar piercing and shearing structures of Dinichthys; in the former 
case true teeth, in the latter only sharpened edges of bone were involved. 
Professor Anthony, of Paris, in his excellent work on arboreal adaptation 
in vertebrates suggests that many of our orders, sub-orders, and families may be 
‘groupings by Convergence’; but in the classification of the Mammalia great 
strides have already been made in the detection of cases of Convergence, as, 
for example, in the case of the extinct Patagonian Sparassodonts. 
5. Recent Investigations on Parasitic and other Eelworms. 
By Gizert E. Jounson, M.Sc. 
Nothing is yet known of the mode of nutrition of the free-living species 
of the Anguillulidw, save of those which are found feeding saprozoically on 
substances putrefying in the soil or in water, or which develop in enormous 
numbers on artificial food-media allowed to decay on samples of soil. These 
species, the majority of which belong to the genus Rhabditis, and are well 
suited to artificial cultivation, find their nourishment among the swarms of 
bacteria which develop in such media and multiply rapidly under these con- 
ditions, though whether they feed on the bacteria themselves or on the products 
of their action is not yet known. The nonsaprophytic free-living species, 
though incapable of being maintained under cultural conditions, may derive 
their nourishment from similar sources but in smaller quantities. 
Those few species of the Anguillulide which have been described as 
parasitic in animals, and of which Rhabditis pellio is the best example, are 
probably not parasites in the strictest sense. 2h. pellio inhabits the common 
earthworm, Lumbricus terrestris, being found in the nephridia in an active, 
and in the celomic cavity in an encysted, larval condition. In this state the 
larve remain without growth or change until the death and decay of the 
earthworm, when they grow rapidly, mature, and reproduce. Rh. pellio, 
though nominally a parasite, is thus comparable in its mode of life with 
the saprozoic species living free in the soil, for it derives the nourishment for 
its growth from decaying organic matter and uses the living earthworm only 
as a shelter during that period when growth is at a standstill. 
The species parasitic in plants (Z'ylenchus, Aphelenchus, and Heterodera), 
pierce the cellular tissue of the plant by means of the hollow stylet protrusible from 
the mouth-cavity and absorb the cell-sap. There are, however, in addition to 
the parasites a large number of ‘ semi-parasitic’ species, which occur in constant 
association with the perfectly healthy plant. They are found chiefly round the 
roots, but, in the case of seedlings of cereal and other grasses, occur also 
between the leaf-sheaths and within the grain from which the seedling is 
growing. Almost all plants appear to have these semi-parasites round their 
roots, attracted from the surrounding soil, which is relatively poor in nema- 
todes. The problem : On what do these semi-parasites feed? remains unsolved. 
Not on the living cells of the root, for most of the semi-parasitic forms are 
unarmed, and the roots are undamaged. Do they feed on bacteria collected 
round the roots? If they feed on bacteria useful to plant growth, they may 
fill a réle similar to that of the Protozoa of the soil, whose harmful activity can 
be checked by the expedient of ‘ partial sterilisation.’ 
6. Some Aspects of the Sleeping Sickness Problem. 
By Professor E. A. Mincury, F.B.S. 
