Prof. P. J. Van Beueden on the Intestinal Worms. 345 



some species of the principal genera of the Trematode and Ces- 

 toid worms; then follow the anatomy and history of develop- 

 ment of these worms. The Trcmatodes are divided into two 

 groups, founded on the mode of life and the development, which 

 appear to be very natural and happily imagined. Some are ecto- 

 parasitic ; they live nearly all on the gills of fishes, and attach 

 themselves by one or even many sucking-disks situated at the 

 back part of the body. 



To these belong Tristoma and Polystoma of Rudolphi, and 

 various other genera adopted by modern writers. They appear 

 to undergo no metamorphosis, and are named by V, Beueden 

 Trcmatodes monogeneses. The second group, of which the genus 

 Distoma may stand as an example, contains the Trcmatodes that 

 live in the interior of the body, and attach themselves by a sucker 

 in the fore part or the middle of their body. They are here 

 named Trematodes digeneses, an a])pellation borrowed from their 

 mode of development ; they proceed from eggs or from germs, 

 in successive and alternating generative stages. 



Of the group of Trematodes monogeneses the author treats 

 of UdoneUa Caligorum, Epibdella Hippogiossi, Ejnbdelta Scicence, 

 V. Beneden, Diplozoon paradoxum, Octohothrium lanceolatumy 

 Octobothrium Merlangi, Axine Belones, Onchocotyle apipendicu- 

 lata, Onchocotyle borealis, Calceostoma elegans, V. Beneden, 

 Gyrodactylus auriculatiis, and Gyrodactylus elegans. Of these 

 worms, Calceostoma forms a new genus, described here for the 

 first time. Calceostoma elegans was found by V. Beneden on 

 the gills of Scicena Aquila. [It must be a typographical error 

 when at p. GO we read, " n'ayant qu'un dixieme de millimetre 

 de longueur;" the figure, pi. 7. fig. 1, of natural size, indicates 

 a length of 10 or 11 mm.] The Ijody is elongate, and has at 

 the fore part a foliaceous expansion, whilst behind it ends in 

 a large sucker, to which a stylet with two pairs of curved hook- 

 lets is attached; the anterior pair turn their points forwards, 

 the posterior backwards ; by these four points the worm is firmly 

 attached to the tissue of the gills of the fish. On Gijrodactylus 

 (a genus of worms that live on the gills of freshwater fishes), V. 

 Beneden confutes the opinion of V. Siebold, that here there is 

 change of generative forms {Generationswechsel). Gyrodactylus 

 is viviparous ; and the young ones, with the two large hooks on 

 the posterior sucker, can be distinguished through the skin 

 within the body of the mother. Two similar embryos, at different 

 stages of development, seen by V. Siebold in a Gyrodactylus, 

 were incorrectly supposed by him to be daughter and grand- 

 daughter, whilst, according to V. Beneden, they were two sis- 

 ters. Here there is no producing by germs, as in the sporocysts 

 of the Distomes. For the Trematodes digeneses, to which Di- 



