ENTOZOA. 187 
Octobothrium LeucKx. (Mazocraes HERM., Octostoma Kun). 
Body soft, elongate, depressed, furnished posteriorly on each side 
with four bivalve acetabula. Mouth anterior, simple. (Mostly two 
anterior acetabula lateral, small.) . 
Comp. Hermann Naturforscher xvit. 1782, pp. 180—182, Tab. Iv. 
figs. 13—15 ; Levoxart Breves animal. Descr. Heidelb. 1828, p. 18, Zool. 
Bruchstiicke 11. 1842, pp. 18—33, Kuuwn Description @un nouveau genre 
de Vordre des Douves, Mém. du Muséum xvii. 1829, pp. 357—3062. Pl. 17 bis. 
These species live on the gills of fishes. The most common is the species 
that lives on the shad (Clupea alosa L.): Octobothrium lanceolatum Luvcx., 
Breves anim. Descr. Tab. I, fig. 7a, 6, Kunn Mém. du Mus. 1.1. figs. 1—3, 
Mayer Beitr. zur Anat. der Entoz. pp. 19 —25, Tab. 111. figs. I.—x. 
Diplozoon NorpM. Body cruciate, as though formed of two 
worms adhering together. Posteriorly four prehensile organs (suc- 
torial acetabula) adhere to each limb on both sides, set upon a 
common dise. 
Sp. Diplozoon paradoxwm Norv. Mikrogr. Beit. 1. Tab. v. vi. (and Ann. 
des Sc. nat. Tom. xxx. Pl. 20). This singular animal was discovered by 
NoRDMANN on the gills of the Bream (Cyprinus brama) ; it is 3—5 lines 
long, and presents a body as if two specimens of Octobothrium had grown 
together in the middle, like the Siamese twins. Other observers also have 
met with this animal on the gills of other species of the genus Cyprinus. 
DusarpIn found very small entozoa on the gills which resembled a half 
Diplozoon, and formed thereof the genus Diporpa; he leaves it undeter- 
mined whether they are young and separate individuals of Diplozoon. 
[This question has been determined in the affirmative by V. StmpoLtp. He 
discovered in the middle of the posterior portion of the body two slender 
hooklets which had been overlooked by Dusarprn in Diporpa and by 
NorDMANN in Diplozoon : they are bent back at an acute angle. Diporpa 
is without sex, and always much smaller than Diplozoon ; it has, moreover, 
behind the middle of the body, at that part where the two bodies of 
Diplozoon coalesce, a sucker, The prehensile organs are much simpler in 
Diporpa than in Diplozoon; but SteBoLD found instances of every inter- 
mediate stage of complexity in them in different pairs of Diporpa which 
had coalesced, so that in some the resemblance to Déiplozoon was in all 
respects exact. After this conjugation or copulation, the generative organs 
appear in the united individuals, and eggs are produced. See C. Tu. V. 
S1eBoLD Ueber die Conjugation des Diplozoon paradoxum, nebst Bemerkungen 
ueber die Conjugations-Process der Protozoen. In Zeitsch. fiir Wissensch. 
Zoologie, 111. 1851, pp. 62—68. ] 
The motion of fluid which NorpmMann thought he perceived in the 
vessels and their branches (in each half of the animal there are on each side 
two principal stems) is according to later investigations to be ascribed to 
vibratile cilia which exist on the inner surface of these vessels and produce 
the appearance of a very rapid current. (EHRENBERG, WIEGMANN’S 
Archiv, 1835, U. 8. 128, MAyER Beitr. z. Anat. der Entoz. s. 23, 24. 
