THE ANATOMY OF POLYPTERUS. 331 
fin-rays. ‘The muscle of the anal fin is greatly enlarged in the male, protruding as a 
rounded mass into the celom. It is this mass which causes the ureters and genital 
ducts to turn so abruptly ventralwards in the male (Pl. L. figs. 2, 5, 6, an.fim.). 
I may mention that in an abnormal male specimen in which the anal fin was absent 
this muscle was completely absent, and the excretory and genital ducts ran backwards 
into an extension of the ccelom, then forwards ventrally to open in the normal position 
behind the vent. 
This sexual character almost entirely disappears out of the breeding-season. 
Leydig has suggested that there is internal fertilization in Polypterus from the fact 
that in the celom of a female Polypterus he found masses of filaments which he took 
for spermatozoa. That these filaments are not spermatozoa can at once be seen by 
comparing the figure he has given with my figure of spermatozoa from the ripe testis 
(Pl. LI. fig. 13). 
When the arrangement of the oviducts is considered, it seems extremely improbable 
that the spermatozoa would find their way into a duct which opens into the urino- 
genital sinus upon a papilla. It remains to be seen to what use the male Polypterus puts 
this modified anal fin. 
IX. The Vascular System. 
The blood-supply to the external gill has been worked out by Hyrtl, while the main 
roots of the arterial system were described by Joh. Miller. I would call attention, 
however, to a few additional details. Having injected a male specimen with salt- 
solution when killed, it was re-injected with a coloured gelatine in the laboratory. 
The specimen was adult and had no external gill. The details of the blood-supply 
to the external gill were made out on a young specimen in which it was possible to 
inject the hyoidean artery with a coloured fluid. The figure of the arterial system was 
made by a combination of these two dissections. 
As Hyrtl has shown, the hyoidean artery arises at the anterior end of the ventral 
aorta immediately in front of the first afferent branchial artery, and passes to the 
base of the operculum, at the centre of which it meets the efferent hyoidean artery, 
to run with the latter to the posterior edge of the operculum and thence to the 
external gill. 
The point I wish to call attention to is that the afferent and efferent arteries at 
the extremity of the gill are continuous one with another, forming a drawn-out 
loop. From the afferent limb branches run to the pinne, at the extremity of 
which they loop back to the main efferent limb; similar tertiary loops pass into the 
pinnules. 
At the root of the external gill there is a dorsal and a ventral muscle ; towards the 
extremity of the gill these break up into numerous isolated bundles (Pl. LI. figs. 
25, 26, 27). The whole arrangement is quite similar to that of an Amphibian or 
Dipnoan external gill. 
VoL. xv.—Part vil. No. 2.—April, 1901. 3A 
