TREMATODA. 
429 
Biology, Evolution. 
Zeller'S paper on Diplozoon (6) throws light on tlie much-douhted 
zygosis ” of the young Biporpm (ciliated and provided with two eyes 
in their first stage) and their subsequent crosswise coalescence into a 
double individual.” Each of the two Biporpcc will seize witli its 
ventral disk the dorsal wart of the other, twisting their bodies in such a 
manner that in the anterior part the dorsal, in the posterior the ventral 
surfaces are turned against each other. Sometimes the copulating individuals 
are of very different ages and sizes ^ and it may happen that one of them dies 
before the complete fusion has taken place, without allowing, however, 
the survivor to extricate itself. After copulation the suckers by means of 
which this process is effected disappear ; and while the Biplozoon increases 
in size, the second, third, and fourth pairs of claspers (if not exceptionally, 
developed before) are formed ; at the same time with the last pair the first 
foundation of the generative organs is laid. In the adult Biplozoon the female 
organs are nevertheless almost invisible during winter ; but they develop 
rapidly if the Blioxini (on the gills of which the observed species occurs) are 
placed in a heated chamber. The eggs are enclosed in corneous operculated 
egg-cases, each produced into a long tortuous filament. 
The observations of Willemoes Sulim (4) are in all points confirmed by Zel- 
ler (5), whose paper on Bolysiomum, however, is much richer in information. 
The eggs have also here operculated egg-cases (without filament), and are 
deposited directly in the water in great numbers. The larva is provided with 
cilia, four eyes, and a circle of sixteen booklets on the posterior part of the 
body ; after the immigration and the loss of the cilia, during the growth of 
the young fluke, the acetabula are developed, pair after pair, the two great 
hooks increase, &c. In the adult the eyes and booklets retain their original 
size, and are therefore easily overlooked; this is also the case in P. occllatwn, 
W. S. (4). Quite young worms are found in great number in young frogs 
of the first year ; in frogs two, three, or four years old their size increases in 
a corresponding degree, but their number declines. The invasion evidently 
takes place only once in the tadpoles, whose branchial cavity was found, in 
the experimental case recorded, highly infested with them, while they did not 
penetrate into any other part of the body. In what manner they afterwards 
migrate into the bladder is still unknown. Old worms, in old frogs, only 
deposit their eggs (no trace of embryo) in spring, during the frog’s visits to 
the water; young worms (2'6 mm., three years old) still contain eggs (with 
mature embryos !) in May and June. 
Anatomy and Physiology. 
Butsciili (I) confirms Stieda’s [and Blumberg’s ; cf. Zool. Bee. viii. p. 454] 
important discovery that the supposed connecting channel between the male 
and female organs does not exist in Ampliistonmm conicuin, but that Laurer’s 
channel” opens freely on the back of the worm, and is, in fact, the vagina, 
in Bistomum endolohum ; it opens on the back in the median line, at a place 
somewhat corresponding to the position of the ventral genital orifice, and is 
connected with ducts from the ovary and uterus, but was found full of moving 
sperm atozoids. A self-fecundation will also probably be found to be impose 
sible in other Trematodes. Zeller (5) arrived at similar results. On the 
1872. [voL. IX.] 2 p 
