M. V. Lebour 
425 
The encysted stage of what is almost certainly the same worm 
occui's in the nerve cord and nerves of various Gadidae, most commonly 
the haddock Gadus aeglejinus L. Williamson (1911, p. 60) has recently 
recorded these cysts from the skin as well as the nerves of Gadidae. It 
was Dr David Hilt Tennant (1906, p. 635) who, working at the life- 
history of the American Bucephalus haimeanus, discovered its identity 
with some species of Gasterostomum, but I doubt if it be the same 
species as the British form although veiy similar. He found the 
encysted stage in the silverside Menidia menidia and the adult in the 
gar Tylosaurus marinus. The cysts in the nerves of the haddock are 
the “Bodies of Munro” of Maddox (1867, p. 87). Thej^ occur parti¬ 
cularly in the region of the auditoiy and spinal nerves. They are also 
common in the cod Gadus morrhua L., and the whiting G. merlangus L.. 
Johnstone (1904, p. 101) records it from the Lancashire coast in Phycis 
hlennioides and also from the cod and haddock. 
The cysts (fig. 3) are oval and thin-walled appearing as little bead¬ 
like swellings along the nerves. Length of cyst 0'60 mm. The 
cercaria coiled up inside is quite colourless with a very conspicuous 
opaque excretory vesicle. When pressed out of the cyst it measures 
about 2'5 mm. m length and is covered with minute spines (fig. 4). At 
about the first quarter of the body is the ventral sucker leading to a 
sac-like intestine. At the anterior end is a sucker-like organ. The 
excretory vesicle is long and naiTOw not reaching quite so far as the 
ventral sucker. A pair of testes is situated obliquely one behind the 
other in the posterior third of the body, the two ducts from these 
uniting in a common vas deferens which is continuous with the 
posteriorly situated vesicula seminalis and cirrus sac, the genital pore 
opening at the hind end of the body. The ovary is situated between 
the testes and the ventral sucker; the uterus and shell gland complex 
are present though not fully formed and no eggs are as yet developed. 
This encysted form is certainly identical with Gasterostomum gracilescens 
which lives in great numbers in the stomach and pyloric caeca of the 
angler LopJmis piscatorius; all stages can be traced in it from forms 
exactly corresponding with the cercaria pressed out of the cyst from the 
haddock to the adult form full of eggs. The angler feeds on fish of all 
kinds, notably Gadoid, and so easily gets the worm into its alimentary 
canal. Nicoll (1909, p. 24) found immature specimens of this worm in 
the stomach of a cod. As he says, it probably got there by its 
sw'allowing some other Gadoid, and almost certainly it w'ould not 
develop any further in the cod. 
Parasitology iv 
■2S 
