382 
Parasitic Worms 
Bahr and Fairley (1920) have confirmed Leiper’s opinion that Schistosoma 
mansoni and S. haematobium are distinct. They found that the molluscan 
intermediate host, Planorbis, can only be infected with Schistosoma mansoni, 
while Bullinus, another intermediate host, is not susceptible to infection with 
that species. Moreover, the cercariae from Planorbis give rise to the rectal 
form of Bilharziasis while those from Bullinus produce the urinary form. 
Another important Trematode, the life-history of which has been recently 
elucidated, is Fasciolopsis buski. Our knowledge of this we owe to Nakagawa 
(1921) who has found that the miracidial larva encysts in species of snails of 
the genera, Limnaea, Planorbis and Segmentina , especially Planorbis coenosus 
and Segmentina largillierti. The cercariae, like those of Fasciola hepatica, 
encyst on grass. 
Amongst other works on Trematode life-histories mention must be made 
of Faust’s valuable work on American and South African forms, Cort’s studies 
on North American larval Trematodes and Jegen’s monograph on Collyriclum 
faba, a Monostome parasite of singing birds. 
The most important work on Cestode development is that of Janicki and 
Rosen (1917) on the life-cycle of Dibothriocephalus latus, a work which has 
evidently given rise to some controversy between the collaborateurs . Rosen, 
in a later publication (1918,' 1919), maintains that the first intermediate hosts 
of the broad tapeworm are the Copepod Crustaceans, Cyclops strenuus and 
Diaptomus gracilis. In addition he found that Cyclops also functions as the 
primary intermediate host of Ligula simplicissima, a common tapeworm of 
aquatic birds. Galli-Valerio (1919) has also added some notes on the develop¬ 
ment of the broad tapeworm. Another tapeworm of the same group, Schisto- 
cephalus solidus, has been shown by Nybelin (1919) to pass its larval stage 
also in species of Cyclops ( C . serrulatus and C. bicuspidatus). 
Perhaps the most interesting‘work on this group of tapeworms, however, 
is that of Okumura (1919) on Sparganum mansoni, a not uncommon tape¬ 
worm parasite, in its larval stage, of man in the East. According to Okumura 
the onchosphere or first larval stage of this parasite develops in the Copepod, 
Cyclops leuckartii. When this is ingested by a mouse or a frog the onchosphere 
penetrates the intestinal wall and develops into the plerocercoid stage in the 
body cavity. This plerocercoid, when swallowed by a dog, develops into an 
adult tapeworm in the dogs’ intestine just as the human Sparganum does 
when similarly ingested, and the adult tapeworms resulting from’ such in¬ 
fections are, according to Okumura, identical. 
The interesting subject of the life-history of Hymenolepis nana has been 
taken up by Joyeux (1920). He has confirmed the belief that this tape¬ 
worm infects without the intervention of an intermediate host but he was 
unable to infect rats by means of eggs from human cases thus apparently 
proving that the human parasite is specifically distinct from the morpho¬ 
logically similar Hymenolepis murina which normally infects rats. In 1911 
Minchin and Nicoll found a cysticercus larva in the rat flea (Ceratophyllus 
