1870. } DR.T. S. COBBOLD ON A NEW ENTOZOON. 13 
and segmentation, then becomes sexual again, and ultimately has the 
power of transforming itself into a Heteronereis. This would signify 
little, perhaps, if the two phases were only slightly different in 
character ; but it must be borne in mind that they represent type 
forms of genera hitherto regarded as utterly disconnected and 
entirely distinct. If Prof. Claparéde’s observations and conclusions 
should be verified and extended by further researches, we shall have 
fallen upon another page of fruitful discovery bearing upon the so- 
called law of “alternate generation.’ In touching upon these genetic 
phenomena, my object is to bring about a probable explanation in 
connexion with the development of the parasitic species now before 
us. From the first, my suspicions were roused by peculiarities of 
structure observable in Acanthocheilonema which forcibly reminded 
me of Dracunculus. Knowing as we do, to some extent, the sexual 
characteristics of this aberrant parasite, and keeping in view, at the 
same time, Prof. Schneider’s interpretation of cognate facts displayed 
by the singular genus Spherularia, it occurred to me that the characters 
exhibited by Acanthocheilonema afforded indications of a new and 
important link in the complex chain of Nematode affinities. Thus 
all the specimens I have examined are females; the oral, anal, and 
reproductive apertures are either entirely obliterated, or, from their 
closure and excessive minuteness, have escaped observation ; whilst 
the whole parasite may be summarily described as an elongated sac, 
crammed from end to end with embryos in all stages of development. 
It should not be forgotten that, for a long time, the mouth and even 
the intestinal tract of Dracunculus escaped detection, and at the 
present hour (notwithstanding Bastian’s remarkable discoveries in 
this relation) the existence of an anal outlet has not been actually 
demonstrated. The alimentary canal of dAcanthocheilonema is 
visible throughout the greater part of its course, but not in the im- 
mediate vicinity of the head. One noticeable difference between the 
two genera consists in the fact that whereas in Dracunculus the em- 
bryos lie free in all stages of growth in the uterine cavity, in Acan- 
thocheilonema they are still surrounded by a chorional envelope. 
Our new species is therefore an ovoviviparous Entozoon belonging, 
like Dracunculus, to that category of Nematodes which are parasitic 
only during the propagative state. It is, I believe, maintained by 
Schneider in the case of Spherularia (his views, however, being op- 
posed to those given by Sir John Lubbock in his admirable memoir 
on this genus), and by Bastian in the case of Dracunculus, that the 
mode of propagation in these wormis is entirely asexual, this opinion 
having received the general support of Prof. Huxley. For my own 
part I wish to say that when, in 1864, with a full knowledge of the 
facts brought forward as regards the Guinea-worm, I offered a contrary 
interpretation of the phenomena, I did so from no other motive than 
that of honest conviction; and even now I hold that an exclusively 
agamogenetic mode of propagation for these worms cannot be suc- 
cessfully maintained. Keeping before us those recent and important 
additions to our knowledge to which I have here called attention, I 
am of opinion that Dracunculus, in the form commonly known, will 
