History of the Nematode Worms. 345 
probably the case also with the smaller specimens of the young 
Ascaris acus. That I have detected the same worm-capsules in 
buzzards with no precedent experimental feeding cannot be 
urged in opposition to my conclusion, as their number was 
constantly comparatively small, even in decidedly older animals. 
I have, however, never met with parasites in the muscles of my 
buzzards. 
The tuberculoid knots consisted of a thin envelope of con- 
nective tissue and an aggregation of cells of considerable size, 
the elements of which were united in the immediate vicinity of 
the worm to form a finely coherent mass, of irregular form and 
opaque texture. It was remarkable that each cyst (at least in 
the lungs) was close to a distinct vessel, and sometimes so firmly 
united to it that it was difficult to separate them. Whether 
this peculiarity justifies us in supposing that the migration of 
the worms is effected through the blood-vessels I will leave un- 
decided; but it appears to me that the circumstance that the 
capsules were generally appended, not to the capillaries, but to 
the smaller arteries, is scarcely in favour of such an assump- 
tion. 
The worms of the muscles of the mole, therefore, present us 
with an example of a Nematode larva which retains its original 
embryonic structure notwithstanding its residence in an inter- 
mediate bearer, and also resembles an embryo in this respect— 
that it recommences its wanderings even after accidental immi- 
gration into a second intermediate bearer. 
These are conditions with which we have not yet become 
acquainted in other groups of Helmintha; but these are not 
the only peculiarities in the life-history of the Nematoda. To 
my great astonishment, I have convinced myself, in the course 
of my investigations, that there are also Nematoda which are 
developed without intermediate bearers*. 
Among these forms is a small Strongylide which is by no 
means rare in the intestinal canal of the dog; it is nearly allied 
to Ancylostomum duodenale of the human subject, and is known 
to zoologists under the name of Dochmius trigonocephalus. Like 
Cucullanus (and Ollulanus), it possesses a horny mouth-armature, 
of cup-like form and complicated structure, with the help of 
which it nibbles at the intestinal villi of its host. 
The ova of this roundworm, which are usually expelled during 
the first stages of segmentation, are developed in damp situations 
in a few days (three to four in summer, four to six in winter) 
* A few months ago, I published a statement of my (first and imperfect) 
observations on the development of Dochmius, Ascaris nigrovenosa, and 
Cucullanus, in the ‘Nachrichten von der K. Gesellsch. der Wiss. zu Got- 
tingen,’ 1865, No. 8. 
