342 Prof. R. Leuckart on the Developmental 
their stay in the intestine not unfrequently extends beyond the 
time necessary for passage. 
But the bleak is not the only bearer of these young Nematoda. 
I have also found them in the pike, and that under circumstances 
which lead me to assume with almost perfect certainty that they 
are the young forms of Ascaris acus, which is well known to be 
so abundant in this fish. 
Beneath the mucous membrane of the stomach of the above- 
mentioned animal we not unfrequently observe white spots, of 
larger or smaller size, produced by an aggregation of cells, and 
which are probably nothing but altered glandular sacs*. Each 
of these cell-masses contains an example of the young round- 
worm just described, and, according to its size, sometimes a 
small one (0°6 millim.), sometimes a larger one (up to 2°5 mil- 
lim.). But, besides the encapsuled specimens, free ones are also 
found, creeping about quickly upon the mucous membrane of 
the stomach and in the intestine, some of which have attained 
to a much larger size. In the intestine I have found specimens 
9 millims. in length; whilst in the stomach none were ever more 
than 5 millims. These larger specimens were indeed always 
sexually immature, but were still distinctly Ascarzdes, and could 
hardly be anything but the common Ascaris of the pike (4. 
acus). The boring-tooth and the wide buccal aperture which 
occur in the smaller worms had been lost, and replaced by the 
large lip-hke projections which were formed beneath the old 
chitinous skin in the circumference of the former buccal cavity 
(as could be distinctly traced in animals of about 3 millims.). 
The preceding observations sufficiently prove that our worm 
is the larva of an Ascaris which undergoes a further develop- 
ment in the intestimal canal of the pike. In the bleak the worm 
retains its original larval organs, although even here it consider- 
ably increases in size. But whether this growth be necessary 
for the further development of the worm in the pike seems at 
the first glance almost doubtful, as specimens of very different 
sizes occur even in the latter ; but, independently of the fact that 
the small worms are almost always found imbedded in the mu- 
cous membrane of the stomach, and very rarely free, it seems 
probable that these smaller forms commence another migration 
after their transfer to their definitive bearer, instead of being 
directly and continuously converted into Ascarides. 
That similar phenomena occur elsewhere among the Nematoda 
is proved by an observation which I have made upon the so- 
called Trichine of the mole. I premise that these so-called 
* Tn the frog, also, numerous capsules of Nematoda are to be found in 
the walls of the stomach and rectum; and these are probably produced 
from altered glandular sacs. 
