BULLETIN OF THE UNITED STATES FISH COMMISSION. 191 



A €0IVTRIBUTI01V TO THE DE VEI.OPMErVT AlVD ITIORPBIOtiOOY OF 

 THE l.OPHOBRANCHIATES; (HIPPOCAMPUS ANTIQUORUM, THE 

 SEA-HORSE.) 



(With ouo plate.) 



By JOHN A. RYDER. 



During" the present summer Mr. W. P. Sauerhoff captured a male 

 sea-borse of our common American species in the Chesapeake, near 

 Cherrystone, !N^orthampton County, Virginia. It was placed in an aqua- 

 rium some time in the latter part of July and shortly afterwards over 

 150 young ones were discharged from its distended marsupium,or brood- 

 pouch. One of these young specimens preserved in spirits and handed 

 to me for investigation is the subject of this notice. 



There is perhaps no teleostean fish which is more grotesquely and 

 profoundly modified in structure as compared with the ordinary ichthyan 

 type than the sea-horse, and it is for this reason that its development is 

 of especial interest to students of embryology. To briefly indicate in 

 what particular features it differs most widely from other bony fishes 

 may not be amiss. 



The caudal fin has completely disappeared and the tail is not even 

 used as a rudder, as in the pipe-fishes, but has become prehensile and 

 serves the animal to hold fast to slender objects in the water. The 

 usual function of the caudal has been assumed by the dorsal and anal ; 

 the dorsal is the principal agent used in i)ropulsion, and with its help 

 the creature sculls along with the axis of its body inclined at an angle 

 of about 45° to the horizon ; the sculling action is undulatory and the 

 dorsal border of the fin describes in its movements a figure like the 

 number 8. The anal appears to play the part of a rudder as well as 

 assist in propulsion. The dorsal is also used in the pix)e-fishes as the 

 propeller ; the body is also inclined when in motion ; their behavior in 

 the water indicates that they have not been as highly specialized or 

 have not undergone such extensive modifications as their relative the 

 sea-horse, but that it is probable that both have descended from a 

 common ancestral type. In both the eggs appear to be received and 

 carried about by the males during the period of incubation; in the male 

 sea-horse there is a marsupium or brood-pouch situated behind the anal 

 fin ; it is comi:)aratively undeveloped except in the spawning season. 

 In some of the pipe-fishes the eggs are carried by the males in an exca- 

 vation or groove in the under side of the abdomen extending for some 

 distance in front of the vent, and covered over by wide dermal folds 

 which arise from either side of the lower edge of the body and which 

 lap over each other in the middle line; in others, as in Syngnafhiis opM- 

 (lion, there is a pouch behind the vent as in the sea-horse. In this space 

 the developing eggs are embedded in a firm gelatinous matrix. Impreg- 

 nation of the ova probably takes place at the time the eggs are trans- 

 ferred from the female to the male. 



