BULLETIN OF THE UNITED STATES FISH COMMISSION. 293 



Messrs. Saiierlioft" and Walke, who were instriiinental iu obtainiug the 

 eggs which were the subjects of the foregoiug study. 



But a few more points iu relation to the development of other portions 

 of the embryo may, ])erliaps, profitably engage our attention. It will be 

 noticed tliat there are over eighty muscular segments or somites repre- 

 sented in the body of the embryo show^u in the egg in Fig. 11. This very 

 large number is unusual in bony fishes at this stage of development; 

 less than half as many are to be observed in the young shad, cod, or 

 mackerel at the same stage. In explanation of this difierence we can 

 only suggest that, since the muscular somites of the adult silver gar 

 are vastly more numerous than those of the three aforementioned 

 species, we should expect the number in the embryo Belone to exceed 

 those of the other species at a very early period, which is found to be 

 the fact. 



The breast fins / are developed early ; the first rudiment api)ears in 

 Fig. 11, and they increase in size progressively from that stage onwards ; 

 at the same time they are gradually pushed farther forwards, and their 

 bases assume a vertical position as in Fig. 16. 



The vent x^ with the growth and prolongation of the tail backwards, 

 communicates with the exterior of the body, as shown in Figs. 11 and 

 16. The iutes ine extends forwards from it, but the mouth will appar- 

 ently not be developed until considerable progress has been made beyond 

 the stage represented iu Fig. 16. There is an embryonic urinary vesicle 

 or bladder, 6, behind and above the vent, which is connected with the 

 segmental ducts anteriorly. The liver is still but slightlj^ developed. 



The mid-brain is the most massively developed portion of the neu- 

 rula, and consists of a pair of large, flattened, saccular outgrowths, 

 which are developed from the upp<'r w^all of the second cerebral vesicle, 

 which partly cover the cerebellum behind antl the lower part of the 

 brain at the sides. The cavity inside the brain is spacious in the em- 

 bryos of Belone, as is indicated in Figs. 12 and 14; the primary vesicles 

 are as yet but little modified in our latest stage. 



Of the history of the development of the unpaired fins, these stages 

 tell us but very little, but there was a slight dorsal and ventral nata- 

 tory fold developed on the tails of the oldest embryos. 



Of the relations of mesoblast to that of the hypoblast and epiblast, 

 we clearly know that the mesoblast of the muscular somites ends 

 abruptly on either side of the body between the upper and lower em- 

 bryonic layers. In Fig. 14 the epiblast and hypoblast are indicated by 

 two diverging lines which end at the sides of the body just in front of 

 the breast fins. 1 his figure show^s in optic section the space between 

 epiblast and hypoblast which runs along the whole length on either 

 side of the body of the embryo. The epiblast amounts up over and 

 covers the embryonic body consisting of the muscular mesoblast, spinal 

 cord and brain, or neurula, and the notochord, segmental tubes and 

 intestine; the hypoblast on the other hand passes beneath all of these. 



