284 BULLETIN OF THE BUREAU OF FISHERIES. 



The farm is divided into two portions: (1) Those parts where the spat is collected 

 and the young are kept to their third year, and (2) the parts where the shells older 

 than 3 years are kept. The breeding season of the pearl oyster is July to August, 

 and before this comes round — namely, in May to June — stones 6 to 8 pounds in 

 weight arc placed over the bottom of the spat-collecting grounds, which are generally 

 in shallower parts, penetrating deep into land. By August tiny shells not more than 

 3 to 4 millimeters long are first discovered, attached to these stones by their byssus, 

 and the number increases steadily with the season. An immense number of shells 

 is collected every year. They are allowed to lie as they are until November, and 

 then those that are too near the shore are removed with the stones on which they 

 are anchored into depths greater than 5 or 6 feet. This is necessary to protect them 

 from cold, from the effects of which they are apt to die in the course of winter if 

 left in the original places. The young shells are then left quietly and allowed to 

 grow for three years, or, better, some may be removed to deeper waters and where 

 they are given more space and get more food, and grow better. At the end of three 

 years, when they are about ."> to 6 cm. across, they are taken out of the water and the 

 operations necessary for inducing them to produce pearls — that is. of putting in 

 nuclei for pearls — are performed on them. At present the number thus operated on 

 in a year is only 250,000 to 300,000. They are then put hack in the sea and spread 

 out at the rate of about 30 to every tsubo (6 feet square), and are left alone 

 for four years more. At the end of that time, or seven years and a half from 

 the beginning, they are taken out of the water and opened. Natural pearls, as well 

 as ■'culture pearls," as 1 have named those produced from the introduced nuclei, are 

 thus har\ ested and put on the market. 



As in all culture enterprises, there are many enemies of the pearl oyster, as well 

 as unexpected difficulties in the way of its culture. Octopus, < '"ilium, Glione (sponges), 

 all sometimes play a sad havoc among the mollusks, hut the most dreaded enemy of 

 all is the ••reil current" or "red tide." This is an immense accumulation of a Dino- 

 flagellata, Gonyaulax, causing discoloration of the sea water, and. in some way not 

 well accounted for. causing in its wake an immense destruction of marine organisms, 

 large and small. 



The "culture pearls" (tig. 1, pi. xi) are, I regret to say. either half pearls or only 

 a little more than half pearls, hut as regards luster, shape, and size, they are beautiful 

 beyond expectations, and meet the requirements completely in cases where only half 

 pearls are needed. 



Pearl-oyster culture is still in its infancy, hut its promises are bright. If, in addi- 

 tion to half pearls, full or "free" pearls can he produced at will, as there are some 

 hopes, it will he a great triumph for applied zoology. 



THE ARK-SHELL, "HAIGAI." 



Area granom Lischke. 



One of the most interesting cultural entei prises in Japan is that with the ark-shell 

 (Area granosa), or "haigai" as we call it. This was originally and is at the present 

 day most extensively carried on at Kojima Bay, near Okayama. This bay opens 



