202 MARIE V. LEBOUR. 
is not described sufficiently to recognise, and D. crassicaudatum seems 
also to be a species of Hemiurus. As Derogenes is a genus closely related 
to Hemiurus it is interesting to find that both inhabit Sagitta as an inter- 
mediate host. 
In Plymouth Sound the only species of Sagitta is S. bipunctata Q. and G. 
In 1916 Mr. Smith called my attention to the number of parasitic nema- 
todes in it from old plankton samples. Afterwards it was found to be 
very common in the fresh samples and quite the commonest parasite of 
Sagita. It is a larval Ascaris, and in all probability is the same species 
as that described by Pierantoni (1913) from Sagitta in the Bay of Naples, 
and he has also found them from Villafranca, Wimereux and Trieste. 
In his brief note on the worm he suggests that it may be identical with 
an Agamonema described by Stossich from a Ranzana, one of the Molide. 
The final host of the nematode from the Plymouth Sagitta is quite un- 
known, but one would expect it to be something common judging from 
the frequency of its occurrence. 
This larval Ascaris occupies the body cavity of Sagitta, lying length- 
wise, and sometimes is three-quarters the length of its host. The figure 
here given (Mig. 1, Plate I) is from a small specimen. The body is colour- 
less and measures 3 to 17 mm. in length and is very narrow. The an- 
terior end is provided with a large larval hook for boring; the cesophagus 
is long and prolonged behind by the side of the intestine into a blind 
cesophageal sac: the intestine which occupies nearly the whole of the 
body, since the reproductive organs are not yet present, gives off for- 
wards a second blind sac, the blind intestine, which runs along by the 
side of the cesophagus. The anus is near the tail, the latter ending in a 
small sharp spike. The brain is plainly seen as a broad band anteriorly 
running round the cesophagus, and just behind it is the excretory pore 
from which can be traced the thin excretory duct. A large proportion 
of the Sagittee brought in by the tow nets is infected with this nematode. 
Two trematode larvee are also common in the local Sagitta, the larva 
of Derogenes varicus (O. F. Miiller) and the larva of Pharyngora bacillaris 
(Molin). Both of these inhabit common fish in their adult state. 
Derogenes varieus is one of the commonest trematodes with a wide 
distribution, and oceurs in a number of different fish. Odhner (1906) 
states that about a dozen and a half northern fish are recorded as its 
hosts. Nicoll (1914) quotes twenty-eight different fish as its hosts from 
the Channel, Coffus, various Gadide and a few Plemonectids are the 
common hosts. It occupies the stomach of these fish. 
Levinsen (1881) records the larval form of this trematode from Har- 
mothoe imbricata, and finds the remains of this annelid in the stomach 
of Cottus, It is very interesting to find the larva in the Sound inhabiting 
