12 DR.T. 8. COBBOLD ON A NEW ENTOZOON. _ [Jan. 13, 
the genus as Tricheilonema; and, indeed, I had already so written 
it, when I afterward found that the late C. M. Diesing had already 
employed the same generic title for a parasite of a somewhat differ- 
ent type. In his final revision of the Nematoda, communicated 
to the Vienna Academy in 1860, he places this Nematode (de- 
scribed in his ‘Systema Helminthum’ as a species of Filaria) as 
the type of his new genus Tricheilonema; whilst, unfortunately, in 
the Introduction or Conspectus of the same revision, this genus, 
Tricheilonema, appears under the synonym of Schizocheilonema. 
This complication of terms is vexatious—the more so since his term 
Tricheilonema would have been much more suitable for the designa- 
tion of our new parasite than for the particular form of Filaria 
there described as having been obtained from the cesophagus of an 
Austrian Snake. On the other hand, since Diesing’s ready method 
makes no pretentions towards a natural classification of the Entozoa, 
and since, also, in the present state of our knowledge, it is much 
more convenient to utilize his system of arrangement than those of 
other systematists, there is the less reason to regret the necessary 
introduction of a new generic term. If Schneider’s system be more 
natural, it is, at all events, much less complete. Without further 
apology, therefore, on this score, I may also remark upon the great 
difficulties surrounding a natural classification of the parasitic Nema- 
todes. The variety of characters they display, especially at different 
stages of their growth, the remarkable disparity of size occasionally 
shown by the sexes, to say nothing of the still more astonishing 
fact that the adult female Entozoon may itself occur in two totally 
distinct forms—all these peculiarities, not to mention many others 
(associated with or depending upon their migratory habits), add to the 
difficulties of taxonomy. These instances of dimorphism, it is true, 
are now no longer believed to be confined to the Nematode Entozoa, 
certain Entomostraca, Aphides, and Bees; nevertheless the recent 
additions on this head are mainly a confirmation of the remarkable 
discoveries of Leuckart and Mecznikow in respect of the life-phases 
and development of Ascaris nigrovenosa. In this connexion one 
may particularize the observations of Prof. Leuckart respecting 
sexual dimorphism as it occurs in Coccus and in Chermes, of Prof. 
Hackel, who finds the naked-eyed Geryoniade@ capable of producing 
(from the walls of the stomach) medusoids totally unlike their 
parents, and of Prof. Claus in respect of the Nematode Leptodera 
appendiculata. It was reserved, however, for Prof. Claparéde to 
discover proofs of the existence of similar phenomena amongst the 
Annelids properly so called. By arecently published brochure (which 
the author has kindly sent me), I gather that the occurrence of two 
distinct sexual forms presented by Nereis dumerilit does something 
more than confirm the statements of the above-named authorities, 
since the dimorphic phases of this singular Annelid have something 
about them altogether peculiar, if not unique*. The sexually mature 
Nereis, we are told, loses for a time its sexuality, increases in size 
* Recherches sur des Annélides (p. 38). Tiré des Arch. des Sci. de la Bibl. 
Dniy. Oct. 1869, 
