24 
E. Ray Lankester, on the Gregarinida, 
centrated towards the centre, after which the envelopes of the 
pseudo-navicells become flaccid, and allow their contents to 
escape, which ^row into Gregarinse, passing through an 
amoebiform stage. As far as Lieberkiihn ascertained, the 
whole process was simply one of gemmiparous reproduction, 
or analogous to it. The pseudo-naviculse were produced by 
gemmation, and the young amoeboid Gregaringe were pro- 
duced from the pseudo-naviculse also by gemmation. The 
pseudo-naviculse of the Gregarinae of the earthworm, which 
are the only species readily attainable for study, are so minute 
that there is great difficulty in defining their contents, even 
with a powerful objective, and it is impossible at present to 
ascertain satisfactorily the structure of those contents. I 
have, however, observed that many pseudo-naviculse have, 
when they have passed some time in the free state, an 
apparently viscid substance occupying the greater part of the 
cavity enclosed by their thick enveloping membrane, while the 
finely granular substance (which is aggregated near the centre 
in most pseudo-naviculse) is deficient. The gradual formation 
of this nucleus of protein matter is described by M. Lieber- 
kiihn, but he does not seem to have observed that in many 
cases it is absent, and that there appear to be two forms 
of these bodies. Is it not probable that the contents of 
these two forms of pseudo-naviculse respectively play the 
parts of male and female elements ? It appears that in no 
other phase of the existence of the Gregarina is there a possi- 
bility of sexual reproduction taking place. The large parent 
Gregarinse have been so carefully watched, and the process 
of ency station so attentively observed, that it may be confi- 
dently stated that under these aspects the Gregarina presents 
no phenomena comparable to those of true sexual reproduc- 
tion, and hence some observers have been led to suppose that 
the pseudo-naviculse pass from the bearer " in which they are 
produced and attain a sexual form in some other habitat. 
Lieberkiihn^ s observations, however, which I have confirmed, 
seem to indicate that in the case of Monocystis Lumbrici the 
changes in the pseudo-naviculse which he has recorded are 
the only ones which take place, and that these occur without 
the intervention of a fresh host. If this view of the case 
should be true the Gregarina which is developed from the 
amoeboid young might be considered as the parent-stock, the 
pseudo-naviculse as sexual zooids, and we should thus have a 
case very easily classed with the other instances of alternation 
of generations. I would, however, merely wish to ofier this 
as a suggestion, since at present we have not, nor, I believe, 
can we have, proof that the contents of the pseudo-naviculse 
are to be regarded as male and female elements. 
