PISCES. 429 



the female Aspredo (Siluroidei) carries the ova attached to the soft ventral 

 skin ; Solenostoma (Lophobranchii) in a pouch between the ventral fins, and 

 formed partly by them ; the male Syngnathidae (LophobranchU] carry them 

 in a sub-caudal pouch ; and in some Siluroidei, e. g. Arius, within the 

 pharynx 1 . The egg-shell in oviparous Elasmobranchii is chitinoid, with an 

 aperture at one end ; usually oblong, with the corners produced into pro- 

 cesses, which are often tendril-like 2 . The zona radiata in Teleostei, and the 

 ovular membranes in other Fish, are perforated by one or more micropyles. 

 The ovum of Elasmobranchii is very large ; of Teleostei, with one large or 

 several smaller yolk-spherules ; of Acipenser, deeply pigmented. Seg- 

 mentation is total but unequal in Acipenser and Lepidosteus, partial in the 

 * ova of all other Fish which are telolecithal. The embryo has a more or less 

 prominent yolk-sac. Larval peculiarities are noticeable, e. g. the external 

 gill-filaments of Elasmobranchii and some Teleostei ; the external gills of 

 Polypterus ; the praeoral disc with suctorial papillae of Lepidosteus ; peculiar 

 spines, bony plates, growths on the fin in many Teleostei. Young Pleuro- 

 nectidae have the eyes normal in position until they assume a horizontal 

 posture in swimming, when one of the two rotates to the opposite side of 

 the head. The Teleostean family Leptocephalidae appear to be arrested 

 forms. 



Fish, like Amphibians, are often sexually mature before they are 

 mature in other respects. Their power of reproducing lost parts is confined 

 to the fins. Many grow as long as life lasts, e. g. for over a hundred years 

 (Carp, Pike) ; others attain a certain standard of size and are short-lived, 

 e.g. Stickleback, Cyprinodonts, many Clupeids. Sexual dimorphism occurs, 

 e.g. the male Teleostean is smaller than the female, and is often brilliantly 

 coloured, temporarily or permanently. The flesh of some forms is poisonous 

 always or at certain times, and is due in many cases to the food. The 

 mucus of the body is often poisonous, and special poison glands are some- 

 times found, e.g. in connection with the dorsal spines of Synanceia 

 (Scorpaenidae), or a perforated opercular spine, as in Thalassophryne 

 (Batrachidae) among Teleostei Acanthopteri. The majority of fish are 

 carnivorous ; some omnivorous ; a few, like the Mullets and Carps, 

 vegetable-feeders. 



Many fish are entirely marine, others exclusively fresh-water, while 

 others again pass indifferently from fresh to sea- water, and vice versa, e.g. 

 Pleuronectes. Some few ascend rivers to spawn, e. g. Acipenser, Salmo ; 



1 The male 15-spined Stickleback (Gasterosteus spinachia) spins a nest for the ova with a con- 

 tinuous thread. The material for the thread is secreted at the breeding season by the epithelium of 

 the tubuli uriniferi and accumulates in the urinary bladder. Mobius, A. M. A. xxv. 1885 ; Prince, 

 A. N. H. (5) xvi. 1885. 



2 In two Australian Rays ( Trygonorhina fasciata, Rhinobatis vincentianus} the shell contains 

 more than one ovum a unique peculiarity; Haacke, Z. A. viii. 1885. The same thing occurs 

 occasionally in the common Hen. 



