608 
ZOOLOGICAL LITEllATUllE. 
but even constitutes a necessary preliminary to further develop- 
ment. Thus in the OUulanus tricuspis (Leuck.) of the cat, which 
is not 1 millim. in length, and produces young of comparatively 
quite colossal size (0*3 millim.), the embryos very soon quit the 
cat^s stomach, some migrating (as in Trichina) into the body of 
their host, and becoming encapsuled. No further development of 
them is seen in the cat; so that here encapsulation is an accidental 
phenomenon, and not the prelude to a further metamorphosis. 
On the embryos being administered to mice, they, however, 
further developed themselves. Nor is OUulanus by any means 
the only Strongylide worm with a change of hosts. It probably 
occurs in several species of Strongylus. 
Cucullanus elegans, — The entire developmental history of 
this worm is given. It is essentially the same (and more 
completely than either in Trichina or OUulanus) as is met with 
in other groups of Entozoa. 
There are, however, also Nematoda which are developed 
without intermediate bearers : an instance is given in Doch- 
mius trigonocephalus of the dog ; the little worms, having broken 
through the outer capsule of the egg, move briskly about in the 
mud ; and without a knowledge of their parentage, they would 
certainly be referred to the IMiabditidas. In about a week they 
have grown to twice their first length, and then their free life is 
at an end. All experiments for the purpose of causing them to 
enter an intermediate host have failed; but they have been 
reared to sexually mature Dochmii in the intestine of a dog. 
Again, there are Nematoda the embryos of which even attain 
sexual maturity in their Rhabditis form, and only become para- 
sitic again in their progeny, as Ascaris nigrovenosa {vide Z. 
Record, 1865, p. 743, and especially Mecznikow^s paper). The 
investigations upon the Nematoda of man present many wide 
gaps. Most of them belong to species with hard and firm egg- 
shells, especially the commoner species, as Trichocephalus dispar, 
Ascaris lumhricoides , and Oxyuris vermicularis. All experi- 
ments of administering ripe ova of Ascaris to dogs, children, 
and adults failed ; and in the face of these, often and carefully 
conducted, the assumption of an infection by means of mature 
ova must acquire more and more improbability. The question 
remains, where are we to find the intermediate host? It would 
appear clear that it is not by any of the larger animals that 
the embryos of Ascarides are conveyed into the intestine of 
their definitive bearer. We now need for the completion of the 
life-history of the Ascarides a single element. May the gap be 
soon filled up, and the commonest of the human Entozoa brought 
within the domain of science ! 
Ascaris nigrovenosa. For the controversy between Leuckart & Meeznikow 
on the subject of the discovery of the development of this worm the reader is 
referred to Meeznikow’s article in Archiv fiir Anat. 1866, p. 409 (translated in 
