aquatic JLiu 



39 



just under the spine. There is a tube 

 called the ureter (25), leading from each 

 kidney. The ureters join and then empty 

 into the urinary bladder (26), which in 

 turn empties into the uro-genital opening 

 (27), situated directly behind the anal 

 aperture. The kidneys filter all waste 

 matter out of the blood as it passes 

 through them ; this waste matter is elimi- 

 nated in solution in the form of urine 



The skeleton is formed of bones com- 

 posed largely of calcium phosphate. Ex- 

 tending from the head to the tail is the 

 vertebral column or backbone (28). This 

 is composed of a number of separate 

 bones, each being called a vertebra. 

 Along the dorsal surface of this spinal 

 column is a groove, in which rests the 

 spinal cord (29). To the backbone the 

 skull or cranium (40) is attached, and 

 along its length a number of ribs (30) 

 project and serve as a protection and 

 support to the body cavity. A small row 

 of bones called the interspinals (31) sup- 

 port the unpaired fins. The pectoral and 

 ventral fins are each supported by a 

 framework of bones called the shoulder 

 girdle and the hip girdle respectively. 



The brain is divided into four principal 

 parts; the cerebrum (^2), the two optic 

 lobes (33) (only one being shown), the 

 cerebellum (34) and the medulla ob- 

 longata (37), which is extended to form 

 the spinal cord. The cord, as has already 

 been mentioned, lies in a groove in the 

 vertebral column, and from this branch 

 most all the main nerves of the body ex- 

 cept some of the sensory nerves. Ex- 

 tending forward from the cerebrum is the 

 olfactory nerve (35) which connects the 

 nostrils. The organs of hearing in the 

 perch are very peculiar, being simple in 

 comparison with the ears of the higher 

 animals. They consist of a closed cavity 

 on each side of the head. Contained in 

 each of these cavities is a small concre- 



tion or stone, made of calcium carbonate 

 and called an otolith or ear-stone, besides 

 the capacity for hearing they are sup- 

 posed to be of service to the fish in main- 

 taining an equilibrium. These otoliths 

 are also found in some of the lower ani- 

 mals, such as the jelly-fishes and some 

 medusae. The sense of taste is not greatly 

 developed. The vision is fairly clear, 

 though at short distances only. 



The muscles of the fish differ from 

 those of the higher, warm-blooded ani- 

 mals in that they are generally white in 

 color and are composed of large flakes. 

 The largest of all the muscles is the great 

 lateral one, reaching the whole length of 

 the body on both sides and controlling its 

 movements. There are also other smaller 

 muscles which control the jaw, eyes, fins, 

 etc. In some fishes, such as the salmon 

 and herring, the muscles are orange or 

 red, but this color is due to the presence 

 of certain oils and not to blood, as in the 

 higher animals. 



The reproductive organs consist of the 

 ovary (38) in the female and the sperm- 

 aries or testes in the male. These extend 

 forward from the uro-genital opening 

 and are connected with it by the oviduct 

 in the female and the vas deferens in the 

 male. It will not be necessary to go into 

 details regarding reproduction, as every 

 aquarist is familiar with both the ovi- 

 parous and viviparous forms. The pro- 

 cess of fertilization of the egg and the 

 development of the embryo is a very 

 interesting study, but space will not per- 

 mit its discussion at this time. 



"I wonder if the little goldfish feels 

 that he is penned up ?" 



"I doubt it. Take my own case. Theo- 

 retically I could go anywhere in the 

 world. Practically I merely swim around 

 in a circle like that fish." — Kansas City 

 Journal. 



