430 
MESSRS. F. M. BALFOUR ARB W. R. PARKER OR THE 
Systematic Position of Lepidosteus. 
A. Agassiz concludes his memoir on the development of Lepidosteus by pointing out 
that in spite of certain affinities in other directions this form is “ not so far removed 
from the bony Fishes as has been supposed.” Our own observations go far to confirm 
Agassiz’ opinion. 
Apart from the complete segmentation, the general development of Lepidosteus is 
strikingly Teleostean. In addition to the general Teleostean features of the embryo 
and larva, which can only he appreciated by those who have had an opportunity of 
practically working at the subject, we may point to the following developmental 
features'* as indicative of Teleostean affinities :— 
(1.) The formation of the nervous system as a solid keel of the epiblast. 
(2.) The division of the epiblast into a nervous and epidermic stratum. 
(3.) The mode of development of the gut (vide pp. 369, 370). 
(4.) The mode of development of the pronephros; though, as shown on p. 420, the 
pronephros of Lepidosteus has primitive characters not retained by Teleostei. 
(5.) The early stages in the development of the vertebral column (vide p. 388). 
In addition to these, so to speak, purely embryonic characters there are not a few 
important adult characters :— 
(1.) The continuity of the oviducts with the genital glands. 
(2.) The small size of the pancreas, and the presence of numerous so-called 
pancreatic caeca. 
(3.) The somewhat coiled small intestine. 
(4.) Certain characters of the brain, e.g., the large size of the cerebellum ; the 
presence of the so-called lobi inferiores on the infundibulum; and of tori semi- 
circulares in the mid-brain. 
In spite of the undoubtedly important list of features to which we have just called 
attention, a list containing not less important characters, both embryological and adult, 
separating Lepidosteus from the Teleostei, can be drawn up ;— 
(1.) The character of the truncus arteriosus. 
(2.) The fact of the genital ducts joining the ureters. 
(3.) The presence of vasa efferentia in the male carrying the semen from the testes 
to the kidney, and through the tubules of the latter into the kidney duct. 
(4.) The presence of a well-developed opercular gill. 
(5.) The presence of a spiral valve ; though this character may possibly break 
down with the extension of our knowledge. 
(6.) The typical Ganoid characters of the thalamencephalon and the cerebral 
hemispheres (vide pp. 381 and 382). 
(7.) The chiasma of the optic nerves. 
* The features enumerated above are not in all cases confined to Lepidosteus and Teleostei, hut are 
always eminently characteristic of the latter. 
