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1 millimeter (1/25 inch) in length, attached to sand grains by the byssus (B). The ssipphon (S) consists of two parts, an incurrent encircle dby twelve tentacles, through which the water enters the mantle chamber of the animal, and an excurrent with four tentacles and filmy telescopic tube through which the water passes out of the mantle cavity. The byssus areises from a gland on the under side of the foot (ft).
Fig.15.--Ciliated gastrula, ten hours after fecundation. The embryo Can now swim through the water by means of hairlike cilia. The larger cells have become invaginated.
Fig.16.--Trochosphere stage, twelve to fourteen hours after fecundation. The body has elongated and the cilia are now confined to the front end. The opening of the primitive mouth (pm) cn be seen on the lower side, while above is a slight indentation corresponding to the eginning of the shell gland (sg).
Fig.17.--Formation of the shell, which arises at two symmetrical points of calcification, right and left of the median line, and gradually envelops the animal.
Fig.18.--Early veliger swimmer with velum extended from the shell, about thirty-six hours after fecundation. aa, anterior adductor muscle, pa, posterior adductor muscle, s, stomach, a, anus, mt, mouth, v, velum.
Fig.19.--Veliger slightly older than shown in Fig.18. The intesting (i) has elongated, and the liver (l) is more prominent.
Fig.1.--Mature egg ready for union with male cell.
Fig.2.--Spermatozoa (male cells). Note length of tail and shape of head. No attempts were made to study the minute anatomy.
Fig.3.--Egg, twenty-five minutes after fecundation, showing the two polar cells (pc) and the faintly developed yolk love.
Fig.4.--Egg just previous to the first cleavage, showing large yolk lobe.
Fig.5.--The two-celled stage at the completion of the first cleavage, fifty minutes after fecundation. The larger cell contains the yolk lobe.
Figs. 6,7,8,9.--This series illustrates the process of cleavage in the egg during the change from the two-celled to the four-celled stage.
Fig.10.--The four-celled stage, one hundred and ten munites after fecundation. Side view.
Figs. 11,12.--The eight-celled stage, one hundred and forty-five minutes after fecundation.
Fig.13.--The sixteen-celled stae, one hundred and eighty-five munites after fecundation. Side view.
Buildings of the Sea Coast Oyster Company at Wellfleet in 1910. The two boats lying at the wharf are typical gasoline oysters dredgers, by means of which the shells are put down for the capture of spat, the grounds are cleared, the see is planted and the oysters gathered for market.
Scallop Pusher.--This implement consists of a wooden pole, from 8 to 9 feet long, attached to a rectangular iron framework, 3 by 1 1/2 feet, fitted with a netting bag 3 feet in depth. The scalloper, wading in the shallow water, gathers the scallops from the flats by shoving the pusher among the eel grass. The photograph shows the correct position of the pusher in operation. Only a small part of the pole is shown
Two scallops, each fourteen months old, illustrate the difference in growth between localities with good and poor circulation of water. The scallops situated in the 'current' receive more food than in the still water, and naturally have a faster growth, as is shown by the greater size of the 'current' scallop
Instrument used for measuring the scallops. The scallop is passed down the trianble until it touches on both sides, where the figures indicate its length in millimeters (25.4 millimeters to an inch). The instrument possesses the advantage of speed and accuracy for quick measuring, as many as 1,200 measurements being possible in an hour
These scallops show two or three lines which indicate temporarily arrested growth. A careful distinction should be made between such lines and the annual growth line, which is caused by the non-growth of the scallop during the winter months, appearing about May 1
Scallop on the left, as indicated by the arrow, has been killed by the oyster drill, which has pierced the shell with a fine hole. A year-old oyster is attached to the scallop on the center, while a Crepidula (quarterdecker) has fastened on the scallop on the right
Young, yearling, and two-year-old scallops. The small scallops on the left are three months old 'seed,' those in the center are eleven months old and have a growth line near the edge of the shell, while the large scallops on the right are twenty-three months old, and have two growth lines, the second being close to the edge of the shell
Scallops: Variation in size of scallops. The two on the left are fifteen months old, while the two on the right are 'seed' scallops three months old. The difference in size in scallops of the same age, especially in different localities, renders impossible the definition of a 'seed' scallop by means of a size limit
Seed scallops, with a small amount of white worm tube (Serpula) attached to the shell. These scallkops have not yet spawned, and, for the future welfare of the scallop fishery, should be protected until they have passed the spawning period, which occurs when the scallop is one year old. The capture of these immature scallops is a decided menace to the fishery, and is forbidden by law
Scallops over one year old, as shown by the formation of the annual growth line, which is caused by cessation of growth during the winter months. Any scallop which does not possess this annual growth line is less than one year old, and is a 'seed' scallop. The present legal definition of a 'seed' scallop is based on the annual growth line, as its absence indicates that the animal has not as yet reached its spawning season, and is, therefor, an immature animal
Method of recording the spawning of the scallop. W.G.Vinal, following the spawning of individual scallops, placed them in separate glass dishes. In this artificial way the time and manner of spawning could be determined, and the eggs obtained for artificial fertilization. Spawning was accomplished by raising the temperature of the water
Spat boxes, lowered from the raft at Monomoy Point, after having been down for the summer. Notice the quantity of barnacles and silver shells (Anomia) which have collected on the outside. Inside, these boxes heavy sets of clams and quahaugs were obtained, while on the outside were found numbers of young scallops, which were removed before the photograph was taken
Oyster drill (Urosalpinx cinerea) boring the shell of a scallop. Five drills were found on the specimen, but one rolled off when the photograph was taken. The drill bores a fine hole through the shell by means of a ribbon-like tongue lined with saw-like teeth, and then sucks out the contents
Nassa obsoleta (the little black winkle of the tide flats) devouring a scallop. These little scavengers swarm over the scallop. Occasionally one is active enough to get between the valves, forming a wedge which permits the entrance of others, which quickly consume the scallop. Owing to the alertness of the scallop and its different habitat (Nassa usually being found on the tide flats) little damage is done
Graphic representation of the growth of the average scallop and its gain in volume. Starting September 1 with 1 bushel of 1/2-inch scallops, the increase in volume is represented on the right in terms of bushels, corresponding to the different sized scallops on the left: (1) two-month scallop, .5 of an inch, 1 bushel; (2) three-month scallop, .91 of an inch, 7.3 bushels; (3) five-month scallop, 1.34 inches, 26.5 bushels; (4) thirteen month scallop, 1.75 inches, 62 bushels; (5) seventeen-month scallop, 2.41 inches, 185.6 bushels.... This repid increase shows the benefit of preserving the 'seed' scallop, as the yield in large scallops will more than repay the fisherman for his foresight
Type of pen used in determining the rate of growth of the scallop. The sizes ranged from 40 to 400 square feet. The posts were made of 2 by 3 foot joists, fixed in the soil and placed at sufficient intervals to hold the netting firmly in position. Wire netting (1 1/4-inch mesh) and old seines of a suitable height were stretched around the posts
Plan of biological raft used at Monomoy Point for growth experiments and spat collecting. The raft, 20 feet long by 10 feet wide, provided with a central well and four trap-doors, was anchored to the Powder Hole in 20 feet of water. Wire cages and wooden boxes were suspended at various depths from the raft. Many kinds of mollusks were caught and raised in these spat boxes. The raft proved particularly useful in the study of the post-embryonic life history, as the scallops 'set' in large numbers on the boxes, cages and ropes, where specimens could be obtained in all stages of development for laboratory examination. Also, many interesting growth experiments upon the quahaug, scallop and clam were conducted in sand boxes
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