350 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1915. 



A comical effect is produced by the waj- in which the little fishes peer at 

 some object, reminding one of the actions of a very near-sighted person. 



Releasing itself at length from its support one may slowly progress still in a 

 vertical position, its tail curved inward, its dorsal fin rapidly undulating, and 

 reminding one of a screw propeller, its pectorals vibrating in harmony. The 

 rapidity of the undulatory or vibratory movements of the dorsal and pectorals 

 is especially notewoi'thy. 



Incased as it is in an almost inflexible coat of mail, progression can not 

 be efiiected by lateral flexion of the body as in ordinary fishes, and flexion in 

 a vertical direction is limited. 



AVith such limited powers of progression a nice adjustment of organs is 

 called for, and Dufosse has exjilained one method. The air bladder is com- 

 paratively large and always distended by a quantity of gas so exactly in 

 harmony with the specific gravity of the body that this entire body is a 

 hydrostatic apparatus of extreme sensibility. A proof of this is that if a 

 single bubble of gas no larger tha-n the head of a very small pin be extracted 

 the fish immediately loses its equilibrium and falls to the ground on which 

 it must crawl till its wound has been cicatrized and a new supply of gas 

 secreted by the internal membrane of the bladder. 



As is well known, the eggs of Hippocampus are taken care of 

 by the male in an abdominal sac or pouch open forward opposite 

 the dorsal fin. The same authority described a peculiar phase con- 

 nected with the breeding habits in these words : 



As the season for reproduction approaches the sexes become prepared for 

 i|-_ * * * Ti^e receptive male's pouch becomes thickened and vascular and 

 thus prepares for the reception of the eggs and the nutriment of the embryos. 

 The males, as usual in fishes, are somewhat smaller than the females. 



Curiosity is naturally excited as to the manner in which the eggs are trans- 

 ferred into the narrow-mouthed ovigerous sac of the male. INIany have 

 watched, but so far as known the only one who has caught the female and male 

 in the act of transfer was Dr. Filipo Fanzago. In May, 1874, the doctor ob- 

 served the approach of the two in an aquarium at Naples. The approach was 

 not once for all, but oft repeated and very short each time. The male remained 

 passive and the egg-burdened female advanced toward him and pressed the 

 aperture for the extrusion of the eggs against the mouth of the male's pouch. 

 At the most a few eggs — perhaps not more than a single one — were passed from 

 the female to the male and then she retreated. After a not very long interval 

 (it varied) she again approached and another transfer was made. Five times 

 Fanzago observed this strange kind of copulation in a short space of time (in 

 breve spazio di tempo), but exactly how long is not stated. He hoped to be able 

 to make further observations, but has left no other records. The eggs are doubt- 

 less fertilized during the act of transfer. 



The ovigerous pouch is especially adapted not only for the reception of the 

 eggs but for the sustenance of the newly hatched offspring. Dufoss6 (1874) 

 found that there was a lining mucous membrane which had the faculty of 

 secreting an aeriform fluid. Further, this function is liable to pathologic devia- 

 tion, in which case the bladder may become stopped up and the fish be unable 

 to control itself and carried to the surface of the water, where it remains help- 

 less till death follows. 



The earliest figures of Hippocampus in 'a printed book, so far as 

 known to the present writer, are those given in Pietro Matthioli's 

 Commentaries on the "Materia Medica" of Dioscorides, which 



