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Show 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. Claparede'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, m y object is to bring about a probable explanation in connexion with the development of the parasitic species now before us. From the first, m y 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 Sphcerularia, 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 Acanthocheilonema is visible throughout the greater part of its course, but not in the immediate vicinity of the head. One noticeable difference between the two genera consists in the fact that whereas in Dracunculus the embryos lie free in all stages of growth in the uterine cavity, in Acanthocheilonema 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 Sphcerularia (his views, however, being opposed 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 worms is entirely asexual, this opinion having received the general support of Prof. Huxley. For m y 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 1 hold that an exclusively agamogenetic mode of propagation for these worms cannot be successfully 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 |
