370 
Ascaricls in the British Museum 
this author, anything from 5 to 37 mm. in length. They have their 
heads embedded in the mucous membrane of the stomach, and in this 
position undergo several ecdyses. When they reach a certain size, he 
considers, they migrate into the intestine of their host and there become 
sexually mature. 
As has been remarked already, the larvae seen encysted in fishes are 
always enclosed within their own cast-off skins. Hence, when the fish 
is swallowed by a seal, and the worms set free from the cysts, it is clear 
that they will still have to rid themselves of these old cuticles, and in all 
probability this does not normally take place except under the influence 
of the gastric juice of the seal. In this way the account of von Linstow 
is brought into accordance with the American authors’ and my own 
hypothesis, viz. that the seals become infected with this Ascarid through 
eating fishes containing the encapsuled larvae. With the further 
supposition that the fishes ingest the eggs of the worm contained in the 
faeces of the seals, we have a fairly complete idea of the fife-history of 
the parasite. Without the aid of direct infection-experiments with the 
appropriate hosts, it is impossible to make the conclusion more certain. 
A summary of the hosts from which the adult A. decipiens has been 
recorded is given by Stiles and Hassall (1899, p. 109). They are all 
species of seals. To this list must now be added Otaria jubata, which 
must, at the same time, be removed from the list of hosts for A. simplex 
Hud. This will leave, as properly authenticated hosts of the latter 
species, only the Cetacea. It seems highly probable that A. simplex 
is restricted to the whales and porpoises, while A. decipiens is parasitic, 
as an adult, only in seals and walruses. 
2. Re-examination of the types of Ascaris similis Baird. 
(PI. XV, fig. 2; PI. XVII, fig. 1.) 
Ascaris similis Baird (1853), p. 19, PL I, figs, la-le; Diesing (1860), p. 656; 
Stossich (1896), p. 69; Stiles and Hassall (1899), p. 146. 
Of this form the only description we have is the original diagnosis 
given by Baird 1 , and there appears to have been no record of the 
occurrence of the worm since 1853. Stiles and Hassall doubt the validity 
of the species, and suspect that it should be included in A. decipiens. 
With a view to deciding this point, I have undertaken a re-examination 
1 This diagnosis is repeated, with only slight verbal changes, in Proc. Zool. Soc., 1853, 
p. 18; and in Ann. May. Nat Hist. (2), xv, (1855), p. 69. 
