10 COMMISSION OF CONSERVATION 



are drawn in with the respiratory current, and swept towards the mouth 

 by cilia on the surface of the gills and palps. 



Breeding. — Of our Atlantic oysters, males and females occur in approxi- 

 mately equal numbers. Each individual, when sexually mature, has an 

 enlarged reproductive organ, situated inside the body and surrounding the 

 stomach, liver and intestine. This organ has two outlets, one on each 

 side, near the posterior end of that part of the abdomen which projects 

 backwards, below the great adductor muscle. Each outlet is the open 

 end of a duct, which runs forward and divides into branches that spread, 

 tree-like, over the side of the body, on their way to the various lobes of the 

 reproductive organ. 



In the female this organ is the ovary, and its duty is the preparation 

 of specialized cells, the ova or eggs, which, as they ripen, are pressed out- 

 wards through the already mentioned duct — the oviduct. Ova are gen- 

 erally extruded in large numbers at a time, constituting the spawn or roe, 

 while the process of extrusion is known as spawning. 



In the male the reproductive organ is the testis or spermary, its duct 

 is the sperm-duct, the specialized cells are sperms or spermatozoa, being 

 also called milt. 



Eggs are spherical, oval or pear-shaped cells of about 1/500 of an 

 inch in diameter, and are barely visible as separate particles to the unaided 

 eye. 



Sperms are extremely small — it would take several thousand to make 

 up the mass of an egg — and somewhat resemble minute pollywogs, in that 

 each has a body and a tail and is capable of independent swimming move- 

 ments. 



When eggs and sperms are spawned into the water on an oyster- 

 bed, many of the eggs are soon met by sperms, one of which may 

 succeed in penetrating into each egg. This is, in brief, what is usually 

 called fertilization. 



The fertilized egg undergoes rapid internal changes, which soon 

 result in its division into two cells instead of one, but remaining in contact 

 and forming one object. Further divisions speedily follow, until the 

 cells become so numerous, their structure so varied and specialized, and 

 their arrangement so orderly that an organized living animal and eventu- 

 ally an oyster is the result. 



The setting apart from the bodies of a pair of adults (male and female) 

 of a pair of special cells (ovum and sperm) which unite (fertilization), the 

 product ultimately becomes a new individual, is sexual reproduction — 

 the only method of breeding and increasing the number of individuals of 

 oysters. 



