NOTES ON SOME CANADIAN INFUSORIA. 303 
separated from the posterior portion; peristome field furrow-like, 
commencing on left side a little distance from the anterior extremity, 
produced obliquely downwards towards the right in a groove formed 
by the oblique curvature of the body, and terminating in a short 
pharynx at or shortly past the middle line; on the contraction or 
shortening of the body, the peristome with the pharynx tor the time 
describes a complete spiral circuit, the animalcule presenting in this 
condition a totally different aspect ; anal aperture postero-terminal ; 
contractile vesicle single, posteriorly located. Inhabiting salt and 
fresh water.” 
With this definition of the genus my observations, although identi- 
cal in most particulars, do not exactly correspond. The points on 
which I differ are mainly the position of the anal aperture, and the 
number of contractile vesicles. On reference to the figure (Pl. 
fig. 1), it will be seen that I have represented the anus (a) as being 
postero-lateral, and I have done so only after having witnessed the 
emission of unconsumed food from that point. Claparéde and 
Lachmann’ did not observe the anus, but merely suppose it to be 
situated posteriorly. Stein,? however, distinctly states that it is 
postero-terminal, and on his authority it is so described above. As 
to the contractile vesicles, I have observed two, one situated in front 
of the pharynx (a.c. v.) and the other (p.c.v.) near the posterior 
extremity but not quite central. On first observing the form I did not 
see the anterior vesicle, probably on account of the constant rotation 
about their long axis which the animals performed, and which, as 
the vesicle is situated slightly in front of the junction of the over- 
lapping anterior portion with the posterior one, would render it liable 
to be overlooked. I, however, lately observed it in one form, but 
having lost it, and having not as yet discovered another, 1 am unable 
to confirm the observation. I would then alter these points of the 
generic definition so as to read, ‘anal aperture posterior ; contractile 
vesicle single or double.” 
The only species belonging to this genus that I have been able to 
find reference to is M. sigmoides, and for it the genus was formed, 
The descriptions of this form vary somewhat, but in no particular 
sufficiently important to establish a new species. ‘The characters of 
1 Etudes sur les Infusoires et Rhizopodes. 1858-1860. 
2 Der Organismus der Infusionthiere. 
