Haswett—A Monograph of the Temnocephalee. 143 
XVI.—AFFINITIES OF THE TEMNOCEPHALES. 
When first discovered Temmnocephala was regarded by Gay as a Hirudinean, and 
the same view was adopted by Blanchard* and by Moquin-Tandon.t — Philippi 
regarded its nearest relative as being Malacobdella. In his “Animal Parasites and 
Messmates” (1876), P. J. van Beneden remarks on Zemnocephala (written Temno- 
Phila):—* This messmate resembles a Trematode by its form and by its posterior 
sucker ; but by its entire character, and especially by its sexual organs, it belongs 
to the Zurbellaria” (p. 47 of the English edition). Semper was the first to set it 
down as an ectoparasitic Trematode, and in this he was followed by myself,|| by 
Weber’ and by Monticelli.** I proposed that it should be regarded as constituting 
a distinct family of the Monogenza, more nearly related to the 7vzstomzde than to 
the others, and in this opinion Weber and Monticelli concur. Braun’stt views have 
already been referred to: he denies the close relationship to the 7vzstomde and 
doubts if the Temnocephalee are completely established as Trematodes. In a 
separate papert{{t he summarizes our knowledge of the family and discusses the 
question whether Temnocephala, regarded as a monogenetic Trematode, is to be 
looked upon as primitive or as degenerate. Brandes{§ also expresses doubts as to the 
correctness of the view that Zemmnocephala is an aberrant Trematode, and directs 
attention to several important resemblances to the ARhabdocela. 
The integument of Zemnocephala and Craspedella is quite exceptional if we are 
to regard them as ectoparasitic Trematodes. A complete distinct epithelial layer 
does not occur in other genera, though in some (/Vz¢schza and Epibdella) as observed 
by Braun|||j such a layer is distinguishable on some parts of the surface, but without 
cuticle or basement-membrane. In the others the outermost layer of the body seems 
rather to correspond to the basement-membrane of the integument of Zesnocephala 
than to a modified epidermis; it is homogeneous, does not readily become stained, 
and seems to be of a resistent character. On the other hand, in this particular 
Temnocephala approaches very near to the Rhabdoceele 7uréellaria; the epidermal 
* Gay’s “‘ Zoology of Chilé” II. p. 51. 
Tt ‘*‘ Monographie des Hirudinés,” p. 300. 
~ ‘Arch, f. Naturg.”” XXXVI. (1870), p. 35. 
§ ‘ Zeitschrift f. wiss. Zoologie,’ XXII. 1872, p. 307. 
|| ‘Quart. Journ. Micro. Sci.’ Vol. XXVIII. (1888); 
‘| “‘ Zoolog. Ergebnisse einer Reise,” etc. 
‘*Saggio di una Morfologia dei Trematodi.” 
++ Bronn’s ‘‘ Klassen u. Ordnungen des Thier-Reichs, Vermes.” 
{tk “Ueber Temnocephala, zusammenfassender Bericht.” ‘Centralbl. f. Bact. u. Paras.’ VII. (1890). 
§§ ‘‘ Zum feineren Bau der Trematoden.” ‘ Zeitschr. f. wiss. Zool.’ LIII. p. 558 (1892). 
\I\| Lom, cit. p. 422, 
