34 OBSERVATIONS ON THE DEVELOPMENT OF RAIA BATIS. 



siderable mass of it, still within the abdominal cavity, remained to be absorbed (fig. 



11, a), where, as in the newly hatched chick, it serves as a 



f nourishment, 



Dr. Davy states that, in the torpedo, the young fish is nourished by the yelk for 



weeks after birth. In all cases we have found the vitelline duct entering the 

 intestine just above the spiral valve. 



Form of the Foetus. — The general form of the youngest specimens is long, slender, 

 and gradually tapers to a point backward, as in fig. 2, and may be described in one 

 word as eel-shaped. The head presents two rounded projections, one of them for- 

 ward (figs. 4 a and 5, d) t forming the foremost part of the embryo ; this is made by 

 the protrusion of the optic lobes, and closely resembles the same part in the embryos 

 of birds ; the second (fig. 5, e) is directed downward, and contains the cerebral 



and olfactory lobes, behind which are the eyes. These last, which in the earlier 

 stages, as in figs. 2, 4, 10, are on the same level with the surrounding parts, soon 

 become remarkably prominent, as in fig. 8, where they remind us of the eyes of the 

 young of Malleus. In the fully formed fish they are again reduced to nearly the 

 same level with the adjoining integuments. As development advances, the optic lobes 

 cease to form the most prominent part of the head, in consequence of a change of 



gans 



position of the cerebral hemispheres, which rise to the same level with the 



just mentioned, as the facial disk (figs. 7, 9, 10, b) advances beneath them. In fig. 6 



the embryo has many of the features of a shark ; and in fig. 8, with the 



pansion 



of the pectoral and ventral fins, it begins to take on the form of the skate. lor 

 further details the reader is referred to the different sections of this article. 



Fins 



In the youngest specimen examined (fig. 2), a vertical fold of skin stretches 

 along the middle line, from near the head almost to the end of the tail above, and 

 from near the umbilical cord to the same point below. These folds do not pass 

 beyond or become connected around the end of the tail. The dorsals ffiM. 2 and 



ly stag 



7, c I are formed by two vertical extensions of the upper fold, and 



of ttax existence are placed midway between the base of the tail and its tip.'which 



last tapers to a slender point. The anals (fig, 2, 7, and 9,0) are formed from a 



similar extension of the under fold, and are situated somewhat farther forward __ 

 are the dorsal, Ihe first (fig. 6, O) growa very rapidl and ^ , ,. 



and If M^ TJ bUt ^ SeC ° nd (% 6 ' *> is ^ *-■«■** Both »**» 

 and lower folds and fins have their edges bordered with follicles. 



Both dorsal and anal fins undergo a very remarkable change as development 

 *7,! te firSt » the ^ .« found quite at the end of the tail, instead 



middle, as in the early stage. This change of relative position seems to be 



