VISCEEAL ANATOMY OF THE CHAEACINID.E. 1] 



the discovery was made, and the precise relations of this c:ij)sule were difficult to deter- 

 mine, but it had every appearance of being completely closed, and no communication 

 could be made out between it and the exterior, cither directly or throug-h the rectum or 

 " bladder." Mr. Stebbing tells me that the situation was unusual for such parasites, but 

 that it is difficult to assign any limits to tlie liberties taken by them with their hosts. 



Summary and Concll'sions. 



The main conclusions to which I have been led in the investigation detailed ia this 

 paper are the following : — 



(1) The ductus pneumaticus has a more or less asymmetric connection with the 

 alimentary canal, not only in tlie Erythrinoids, in which it has been long recognized, but 

 also in the Characinidoe generally, in the Cyprinidie, the Gymnotidse, the Siluridte, the 

 Salmonidse, the Esocida?, the Mormyridse, the Notopteridte, the Galaxiid?f:, the 

 Percopsidse, the Cyprinodontida?, and perhaps other families. 



(2) This asymmetry is to the left side in certain families of fishes, and to the right side 

 in certain others. 



(3) In many families, including some of the most primitive and generalized, no 

 asymmetry exists, the duct being median. 



(4) The evidence furnished by the whole series of observations seems to point to the 

 derivation of the asymmetric condition from a pre-existing symmetric or mid-dorsal 

 position of the duct, this being contrary to the view advanced by Sagemohl, who 

 regarded the Erythrinoid condition as being archaic. 



(5) In certain fishes — ^otopterus and Fetrocephalus (a Mormyroid) — the ductus 

 pneumaticus has also an asymmetric connection with the air-bladder. 



(6) The posterior sac of the air-bladder presents in the Characinidse a characteristic 

 arrangement of longitudinal ligaments or septa. The similarity of these septa amongst 

 the members of some natural groups, such as the Ichthijoborince, suggests a cartain 

 constancy in this character, which may be found to be of systematic value. On the 

 other hand, the part played by tliesc septa in the formation of a cellular air-bladder in 

 Enjthrinus, and especially in Lebiasina, together with their existence in varying degrees 

 of development, suggests that they jiossess a significance as a vestige of a formerly 

 cellular bladder in the ancestors of the family. 



(7) The ovaries in the Characinidue arc closed sacs, without communication with the 

 body-cavity. This statement, which is, however, based upon the examination of a limited 

 number of genera, is in accordance with the statements of Joli. Miiller and of Sagemohl, 

 but is at variance with some of the assertions made by Valenciennes. 



(8) I have described two soracAvhat diiferent ovarian conditions, of which Scircodacen 

 and Alestes respectively may be taken as typical, the difierenco lying in tlie degree of 

 backward extension of the ovaries. Both cystoarian *. 



* Huxlej-, T. H., "Contributions to Morphology — Iclitliyopsida. No. 2: On the Oviducts of O.^menis, with 

 Remarks on the delations of the Tcleostoan with the UanoiJ Fishes," Proc. Zool. Soc. Lond., lSS:j. — Howes, (i. Jj., 

 " On some Hermaphrodite Genitalia of the Codfish (Gtidus morrhua), wilh llfmarks upon the Morphology and 

 rhylogeny of the Vertebrate Reproductive System," Journ. Linn. Soc, ZooL, xxiii. Ib'Jl. 



