532 DR. DAVY ON THE TORPEDO. 



attached to the ovaria, they are covered with a vascular membrane, through which 

 they break to enter the infundibulum. In the uterine cavity they are destitute of 

 white ; they are covered, before the appearance of the embryo, with a most delicate 

 membrane or pellicle, and consist entirely of yolk. The number of eggs varies very 

 much with the size of the fish : in the smallest pregnant fish that I have examined, I 

 have never found fewer than four in the two cavities ; and in the largest, not more 

 than seventeen. Their size, too, varies ; — their average weight is about 182 grains ; 

 the largest of eighteen eggs which I have weighed, taken from five different fish, 

 before the embryo appeared, was equal to 210 grains, the smallest to 129. Though 

 without a distinct white, there is, in the uterine cavity common to all of them, a little 

 fluid, generally milky, more rarely glairy, and sometimes bloody, which on evaporation 

 affords crystals of common salt and a very little animal matter, composed chiefly of 

 albumen. 



In describing the foetal development of the Torpedo, I shall confine myself strictly 

 to what I have actually observed. 



In the first stage in which I have witnessed the embryo, it appeared as represented 

 in Plate XXII. fig, 1., about seven tenths of an inch long, without fins, or electrical 

 organs, or any distinct appearance of eyes, with very short external branchial fila- 

 ments*, not yet carrying red blood, and with a red spot in the situation of the heart 

 (probably the heart itself) communicating, by red vessels in the umbilical cord, with 

 the vascular part of the egg. 



In the next stage in which I have observed it, it appeared as in Plate XXII. fig. 2., 

 not quite an inch long, nor a quarter of an inch wide ; the ventral fins visible, and 

 also the dorsal and the inferior portion of the great pectoral fins ; the branchial car- 

 tilages distinct and naked, the electrical organs not having yet appeared ; the external 

 branchial filaments longer than in the preceding, but still comparatively short ; some 

 of them tipped with red blood, others carrying it. 



The next stage of advance I have seen is represented by fig. 3. Plate XXII. This 

 embryo was about an inch and one tenth long and four tenths of an inch wide where 

 widest, and it weighed just five grains. Its electrical organs were beginning to appear. 

 The external branchial filaments were about six tenths of an inch long and contained 

 red blood. The heart was distinct and large, as were also the two lobes of the liver. 

 The stomach was small, apparently empty, smaller than the intestine : the intestine 

 was large and white. The vitello-intestinal canal was distinct ; it appeared as a 

 very slender thread, connected with the upper part of the intestine, and, like the in- 

 testine itself, it contained no yolk. The eyes were apparent. There was a vesicle 

 on the head distended with a colourless fluid, and the cavity of the cranium was full 

 of a similar fluid. The roots of the electrical nerves were visible, but no brain. 



The next stage in which I have observed the embryo is represented by fig. 4. 



* These filaments, variable in length and appearance, are constant in containing each a blood-vessel, which 

 makes the circuit of the filament. 



