44.7 
XLIX.—On the Developmental History of the Nematode 
Worms. By Rupo.tew Leuckarr. 
[Continued from p. 347.] 
I am acquainted with phases of development similar to those 
last described in Sclerostomum equinum, the notorious palisado 
worm of the horse (Strongylus armatus, auctt.), not, however, 
from the intestine, in which I have always found the worm in full 
sexual maturity, but from aneurismatic dilatations of the mesen- 
teric arteries, which are produced by the parasitism of this ani- 
mal, and frequently (when great numbers are present) increase 
to a very considerable size. Contrary to what occurs in the in- 
testine, we find in these aneurisms nothing but young forms of 
the worm (the so-called small variety), from which I am inclined 
to think that the worm passes only thence into the intestine, 
probably through the peripheral ramifications of the mesenteric 
arteries. If my supposition be well founded, the worm must 
certainly bore through the wall of the intestine at a time when 
it is already of the considerable length of 15-20 millims. (thick- 
ness=1 millim.); but the powerful armature of the mouth, and 
especially the denticulation of the margins of the lips, which 
almost involuntarily remind one of a trephine, show that this 
process cannot be attended with any great difficulties. 
The youngest of the worms detected by me (as also previously 
by Mehlis, Gurlt, and Dujardin) in the aneurisms had a length 
of about 10-12 millims. From their grade of development, 
they might be compared with the intermediate forms of Doch- 
mius and Cucullanus, although differing from these not only by 
their larger size, but also by the want of the buccal cup. In- 
stead of the latter, the worms (like the young forms of Ollu- 
lanus) possess in the periphery of the gaping buccal orifice a 
rosette-like plate with six lamine, which exhibit an elegant 
sculpture. The caudal extremity is short and pointed, and, 
in the small specimens, of perfectly concordant structure ; 
whilst among the larger worms we may distinguish specimens 
with slenderer tails, and others with a shorter and plumper 
posterior extremity. In the former the tail is longer than 
broad; in the latter, on the contrary, broader than long, and 
truncated at the apex (which is directed dorsally). 
If we subject the latter specimens to a closer examination, we 
at once find that they are the male animals. However, we are 
led to this conviction less by the still rudimentary internal 
sexual organs than by the copulatory apparatus, which is deve- 
loped beneath the cuticular covering of the inflated posterior 
extremity, and becomes more and more recognizable with in-, 
creasing age. 
