DR. DAVY ON THE TORPEDO. 533 



Plate XXII. It was advanced only a little beyond the preceding ; the principal 

 differences were in the electrical organs being a little larger, the branchial filaments 

 considerably longer (about an inch long), and the brain and spinal cord apparent. 



In the next stage in which I have seen it, as represented by fig. 5. Plate XXII., 

 there was a very considerable advance. The foetus was about two inches and a half 

 long, and one inch and three quarters wide. The electrical organs were distinct, the 

 pectoral fins entire, the external branchial filaments very long. The stomach was still 

 small, and empty, whilst the intestine was distended with yolk. The external yolk was 

 covered with a vascular membrane, and not partially, as in the preceding, but en- 

 tirely. The vitello-intestinal canal freely communicated with the intestine, and was 

 yet very little enlarged where it joins itself to the intestine at the commencement 

 of its valvular portion. 



The next stages which have come under my observation are represented by 

 figg. 6 and 7- Plate XXII., and fig. 1. Plate XXIII. The cavity of the abdomen is 

 shown laid open in figg. 6 and 7? in order to exhibit the external yolk in progress of 

 diminution, and the internal yolk contained in a membranous bag, as it were, a late- 

 ral extension of the vitello-intestinal canal, in progress of accumulation*. The bran- 

 chial filaments have almost entirely disappeared. 



I shall notice only two stages more of the young Torpedo, represented by 

 fig. 4. Plate XXIII., and fig. 1. Plate XXIV. ; the one of a fish six weeks old, in which 

 the internal yolk was considerably diminished in bulk, its connexion with the um- 

 bilicus almost absorbed, the intestine full of yolk, the stomach empty but consider- 

 ably developed : the other of a fish six months old, in which only a very small por- 

 tion of the internal yolk remained, and the connexion of the inner yolk-bag with the 

 umbilicus was absorbed, a vestige only of the canal of communication remaining. 



These fish, at about the full period of utero- gestation, were extracted from a Tor- 

 pedo just after she had been caught, were instantly put into salt water, and were 

 preserved alive. I shall have occasion to revert to them in another part of my 

 paper. 



I may remark generally, that I have never found in any of the gravid Torpedos 

 which I have examined in diflferent stages, any membrane investing the foetus, as is 



* At this period of foetal development the yolk has two distinct membranes, an external transparent one and 

 ui internal vascular one. The former is of great delicacy generally, excepting where the egg joins the abdo- 

 men ; there it is very thick and strong, and slightly opake, serving in a manner the part of the sheath of the 

 umbilical cord of the Mammalia : it is connected with, and appears to end in the cutis of the abdomen. The 

 latter, the membrana umbilicalis, or chorion, if it may be so called from its great vascularity, passes into the 

 cavity of the abdomen, and terminates in the vitello-intestinal canal, from whence the internal yolk-vesicle pro- 

 ceeds. Two large vessels (the trunks of the vessels of the chorion) enter the cord-like termination of the egg: 

 one of them terminates in the vena portae ; the termination of the other I have not ascertained in a satisfactory 

 manner ; I believe it corresponds in function to the umbilical arteries, and brings blood from the foetus to the 

 egg, the other vessel returning it. 



MDCCCXXXIV. 3 Z 



