404 
Tapeworms of Birrls 
In making infection experiments with Entomostraca the same result 
was observed (7). The presence of many tapeworms caused a heavy 
mortality amongst them, and even a few worms had an appreciable 
effect. The explanation seems to be as there stated, that the Cestodes 
secrete a toxin which, when present in large quantities, acts as a strong 
poison, but which may have no apparent effect when diluted. 
The onchosphere when swallowed by the brandling is a roughly spheri¬ 
cal body 0-03 mm. in diameter (PI. XIX, fig. 6). Without any apparent 
internal change it increases in size to 0-053 x 0-048 mm. and about 
that stage is liable to lose the embryonic hooks (PI. XX, figs. 14, 15). 
Sections of this stage show it to consist of a mass of cells of two distinct 
sizes surrounded by an exceedingly thick membrane (PI. XIX, fig. 7, m.). 
Several internal cavities next appear and grow until they coalesce 
(PI. XX, fig. 17), occupying the whole centre of the cysticercoid, the 
cysticercoid being a mere hollow shell of tissue, still surrounded by a 
membrane but one not nearly so thick as before. Sections show the 
membrane to be structureless. Inside it is a thin layer of parenchyma 
with large nuclei disposed in a circle along its inner limit. A slight 
thickening can be observed at one pole. This was the highest point 
of development reached in the experiments. 
At an early stage, while still provided with its embryonic hooks, 
the onchosphere penetrates the intestinal wall of its host and comes to 
rest in the large hepatic cells of the typhlosole. As it grows in size it 
necessarily distorts the intestine and causes internal change generally. 
The worms figured in PI. XX, figs. 18, 19 were exceedingly heavily 
infected, having about 20 cysticercoids in an inch of the intestine. 
The intestine becomes distorted, the cavity ( i.) almost obliterated. 
There is no trace of typhlosole and no distinction between the two 
cellular layers. Dorsal and ventral blood-vessels, if present at all. 
are usually too minute to be seen. The nerve-chord is pushed against 
the ventral body-wall. There are numerous corpuscles in the coelome 
but not as many as usual. A curious feature is that the cysticercoids 
lie loose in the intestinal wall of the host and are not attached to it. 
In dissecting the earthworm a prick of a needle in the exposed intestine 
was usually sufficient to liberate 10 to 30 cysticercoids. 
Chocmotaenia farina Duj. 
The specimens of Choanotaenia farina Duj. were obtained from a 
number of sparrows. They varied in length from 55-66 mm. (Clerc, 
50 mm.), their greatest width was 1-15-1-3 mm. (Clerc, 0-8 mm.). The 
