13i Observations on different points of (lie Natural History 



had the advantage of being able to consult all the works of dif- 

 ferent American Ichthyologists who may have written on the 

 subject ; but I invite these gentlemen, if they have not already 

 done so, to examine the males of the American species, and to 

 study the anal fin of this sex. Perhaps there might be some- 

 thing to rectify in the M. latipinna : as to the Hydrargyras, I 

 know nothing of the male sex. It would be perhaps necessary 

 and useful to count again with the greatest care, and on many 

 individuals, the number of branchial rays. 



I have also described in my "Memorias" a species of Lepidos- 

 teus (in English Gar-pike), to which I left the vulgar name of 

 Manjuari. The animals of this species, intermediate between 

 reptiles and fishes, have become celebrated from the point of 

 view under which M. Agassiz has considered them ; and the 

 stud)' - of their swimming-bladder may throw some light on the 

 function of this organ, so little known ; and particularly on the 

 mode of respiration of the Lepidosteus. As the fresh waters of 

 the United States contain different species of this genus, it 

 would be desirable to have the Ichthyologists of that country 

 examine this subject ; because my studies do not enable me to 

 decide this important question. I here confine myself to the 

 exposition of different facts observed after the publication of 

 my "Memorias," and to inquiries addressed to scientific men on 

 the consequences which I should deduce from them. 



The swimming-bladder of fish has been shown by different 

 authors (see the Precis d'Anat. Comp. of M. Ilollard), to be a first 

 approach towards the abdominal appendices of the serpents, and 

 the aerian sacks of birds ; but none of them, so far as I know, 

 have as yet proved it to be supplementary to the respiration of 

 fish. However, seeing that ordinarily the bladder presents, 

 besides the red bodies which secrete the gas, beautiful vascular 

 nets of sundry colors, displayed on the internal membranes, — 

 at times united to the surface of the organ, at others detached, — 

 one is almost tempted to believe that there is an absorption of 

 oxj'gen produced by th 3 red body. However this may be, no 



