TREMATODA. 
Verm. 11 
10. ViLLOT, A. Sur I’appareil vasculaire des Trematodes [on the 
excretory or vascular system of Distoma insigne\ 0. R. Ixxxii. 
pp. 1344-1346. 
11. Zeller, E. Weiterer Beitrag zur Kenntniss der Polystomen. 
Z. wiss. Zool. xxvii. pp. 238-274, pis. xvii. & xviii. 
A note on Distoma gigas, by G. Nardo, Atti Inst. Yen. (5) i. 
pp. 265 & 266. A paper by R. H. Fetz on the anatomy of the elephant’s 
fluke {D.jachsoni)f in the “ New York Medical Journal,” is cited, Yeteri- 
narian, 1. c. p. 854. 
Anatomy, Evolution, &c. 
Zeller’s continued studies (11) of Polystomum integerrimum have led 
to remarkable results. From the testis, two seminal ducts take their origin ; 
the longer goes to the copulatory organ, by the means of which the 
sperma is introduced into the body of the fellow-fluke during copulation ; 
the other, and shorter duct communicates with the canal leading from 
the ovary and from the yelk-producing organ. To this communication, 
the possibility is due of an internal self -fecundation in such individuals 
as live a solitary life in the bladder of the frog, if self-copulation 
should prove ineffectual. The mutual copulation between two individuals 
is easily observed ; the cirrus of each is introduced into one of the small 
orifices of one of the two “ lateral pads ” of the other individual, and 
the spermatozoa thus conducted through a special canal to the common 
canal, leading from the ovary and from the organ which produces the 
cells of the “ nutritive yelk.” They are therefore mixed with this sub- 
stance before they come in contact with the “ovula;” these three elements 
are then carried together to the uterus, by the peristaltic movements of 
which the egg gets its definite constitution and external covering, the 
material of the shell being furnished with peculiar glands, opening in the 
duct immediately behind the uterus. The fully -formed eggs accumulate 
(sometimes in great numbers) in the oviduct, and are expelled through 
the genital opening common to both sexual systems, the flukes protrud- 
ing themselves half way into the cloaca of the frog during this operation. 
Under ordinary conditions, the eggs are laid in spring, when the frogs 
awake from hibernation and resume the work of reproduction, and the 
larvae are hatched at a period when the tadpoles are in a somewhat 
advanced state of evolution. They migrate into the branchial cavity, 
where they take their abode for about two months ; when the gills of 
the frog begin to disappear, they migrate through the oesophagus anc^ 
intestine to the bladder ; their whole cycle of development until sexual 
maturity takes three years. On the other hand, when the formation of 
the eggs and the evolution of the larvas of Polystomum are artificially ac- 
celerated, e.g., by keeping the frogs in heated rooms, the larval Poly- 
stoma are hatched at a period when the tadpoles are still quite young, 
their gills delicate and soft, etc. Their evolution is then very rapid, they 
become mature and produce eggs within five weeks ; their life is at end 
before the gills of their hosts are obliterated, and they never migrate 
into its internal organs. But these “ gill-cavity ” constitute 
