508 
NATURE 
[ Oct. 26, 1871 

still, of course, remains to show /ow the homoplasy has 
been brought about. In some cases, as in the homoplastic 
forms of American Cactacez and South African Euphor- 
bias, or in the stipular bud scales of many wholly un- 
related deciduous trees, the nature of the similar external 
conditions may possibly be made out with some correctness. 
Again, Dr. Seemann has pointed out that by the rivers in 
Nicaragua and in Viti, the vegetation, although composed 
of very different plants, puts on the willow form 
(“ Dottings by the Roadside,” p. 46). A phenomenon true 
of two distant places accidentally contrasted, might be 
expected to obtain more generally ; at any rate, among our 
indigenous riparian plants Lythruwm Sacicaria and the 
willow-herb are, as their names indicate, additional illus- 
trations. The band of vegetation that fringes a stream 
is always densely crowded with individual plants, and it is 
easy to see that elongated and vertically disposed leaves 
would be most advantageous, exactly as they are to the 
gregarious plants of meadows and plains. The homo- 
plastic agreement of riparian plants may be therefore a 
direct result of selective effort due to the position in which 
they grow. 
In other cases the operation of similar external mould- 
ing influences is not so easy to trace. It might, perhaps, 
however, be imagined that plants would hereditarily re- 
tain the effects when the influences had ceased to 
operate, and no new ones had come into operation pre- 
cisely adapted to obliterate the work of those that preceded 
them. Suppose, for example, that willows got their habit 
and foliage from ancestors that were exclusively riparian, 
then any descendant that happened to be able to tolerate 
situations with less abundant supplies of moisture, would 
not necessarily lose their characteristic foliage on that 
account. Such races fhight be expected to occur near 
rivers subject to periodic droughts, since under these con- 
ditions any others would be likely to perish. Under such 
circumstances we should have cause and effect no longer 
in contiguity ; the riparian habit surviving the riparian 
situation. 
I suggested at Edinburgh that possibly similar habits 
in plants might be bronght about by afferent causes. This 
was only asuggestion, and probably what has just been 
said is a truer account of the matter. At any rate the 
illustration I gave of my meaning has been quite mis- 
understood (as, for example, in the last number of the 
Popular Science Review). It is well known that there 
are a certain number of plants indigenous to the British 
Isles, which are found at a considerable height upon 
mountains and also upon the sea-shore, but not in the 
intervening space. In the latter situations they contain 
more sodium salts than in the former, and inasmuch as 
these salts are destructive to many plants, those that 
compose a strand flora must be able to tolerate them, and 
this of course is an advantage, because many of their 
competitors are poisoned off. Similarly plants of moun- 
tains must have a similar advantage over others in ability 
to tolerate mountain asperities uf climate. Now, suppose 
a mountain submerged ; its flora and certain portions of 
that of the strand come to coincide. Then if we suppose 
the mountain gradually to emerge, some of these plants 
will spread downwaids under the uncovered surface, 
and travel over the whole of the interval that ultimately 
separates the mountaintop and the strand. Why, then, 
do they not remain there? Simply, I believe, because 
they are elbowed out by other plants which, nevertheless, 
cannot tolerate the conditions of life either on the moun- 
tain or the shore, and leave these, therefore, as refuges 
which they are unable to invade. It is possible that the 
action of similar soil constituents might help to bring 
about homoplastic agreements in plants. The sug- 
gestion is not, however, one that occurred to me to 
make. My object was simply to show how two perfectly 
different causes might produce the same effect, namely, 
that of giving immunity from competition to a small 

group of plants. Except as an illustration of this point, 
the matter was quite irrelevant to the subject about which 
I was speaking. W. T. THISELTON DYER 

ON THE DISCOVERY OF STEPHANURUS IN 
THE UNITED STATES AND IN AUSTRALIA 
HE time has now arrived when a full statement of 
the facts relating to this interesting parasite. Stepha- 
nurus dentatus, should be made more generally known ; 
for not only is the progress of helminthological science 
likely to be checked by delay in this matter, but, in the 
absence of definite information, the several merits of the 
original discoverer and describer of this entozoon are 
likely to be altogether ignored. I therefore record the facts 
and inferences in the order in which they have recently 
come under my notice. 
On the roth of January last, through the firm of Messrs. 
Groombridge. I received an undated communication from 
Prof. W. B. Fletcher, of Indianapolis, Indiana, U.S.A. 
In that letter Dr. Fletcher announces that he has “ found 
a worm” infesting the hog, and he helps one to realise its 
abundance by adding that he obtained it “in nine out of ten 
hogs” which he examined. After recording some other 
important facts respecting the tissues and organs which 
were most infested by the parasite, Dr. Fletcher remarks 
that he cannot find any description of the worm in the 
work on Entozoa issued by the publishers above men- 
tioned, nor in the writings of Von Siebold and Kiichen- 
meister, and he therefore encloses specimens for my 
determination, requesting a reply. 
As I have already stated in my first letter recorded in 
the British Medical Fournal (for January 14, p. 50, where 
many other particulars are given which I need not here 
recapitulate) I was instantly struck with the “strongyloid 
character ” of the fragmentary and shrivelled up specimens, 
and I may also add that it at once occurred to me that I 
had had some previous acquaintance with a scientific 
description of the worm. Proceeding, therefore, to turn 
over a series of helminthological memoirs, for many of 
which I stand indebted to the late veteran, Dr. K. M. 
Diesing, of Vienna, I soon had the good fortune to find 
the desired record. The memoir in question forms part 
of the “ Annalen des Wiener Museums” for 1839, the full 
title being “ Neue Gattungen von Binnenwiirmern, nebst 
einen Nachtrage zur Monographie der Amphistomen.” 
As this work is probably little, if at all, known in the 
countries now necessarily most interested in the history 
of this entozoon, I cannot, perhaps, do better than 
transcribe Dr. Diesing’s brief notice of the original dis- 
covery, together with his description of the external 
characters presented by the worm. After naming the 
parasite Svtephanurus, on account of the coronet-like 
figure of the tail of the male, and giving a technical 
description of the species, he continues as follows :—“At 
Barra do Rio Negro, on the 24th of March, 1834, Natterer 
discovered this peculiar genus occurring singly or several 
together in capsules situated amongst the layers of fat, in 
a Chinese race of Sus scrofa domestica. Placed in water 
or in spirits of wine, they stretched themselves considerably, 
and almost all moved up and down.” 
“The males measure from ten to thirteen lines in length, 
the females from fiiteen to eighteen lines, the former being 
scarcely a line in breadth at the middle of the body, whilst 
the Jatter are almost a line-and-a-half in thickness. The 
curved body thickens towards the tail, is transversely 
ringed, and when viewed with a penetrating lens, is seen 
to be furnished with integumentary pores. The oral 
aperture opens widely, and is almost circular ; it is sup- 
plied with six marginal teeth, two of which, standing 
opposed to one another, are larger and stronger than the 
rest. The tail of the male, when evenly spread out, is 
surrounded by a crown of five lancet-shaped flaps ; the 
combined flaps being connected together from base to 
