. Introduction to zoology; a guide to the study of animals, for the use of secondary schools;. rick. overlies the brain. Note the largeeyes, which are yet without pig-ment. Embryo about 21 days 25. From Herrick. swimmerets. On account of its resemblance to the Schizop-oda, the larva at this stage is known as the Schizopodlarva (Fig. 115). In moulting for the fourth time, theexopods are lost from the future walking appendages, andthe animal resembles a lobster except for its small size (). During these early moultings the young lobstersundergo a terrible mortality, so that out of
. Introduction to zoology; a guide to the study of animals, for the use of secondary schools;. rick. overlies the brain. Note the largeeyes, which are yet without pig-ment. Embryo about 21 days 25. From Herrick. swimmerets. On account of its resemblance to the Schizop-oda, the larva at this stage is known as the Schizopodlarva (Fig. 115). In moulting for the fourth time, theexopods are lost from the future walking appendages, andthe animal resembles a lobster except for its small size (). During these early moultings the young lobstersundergo a terrible mortality, so that out of ten thousandembryos hardly two, on the average, survive. After the THE CRAYFISH AND ITS ALLIES 117 fifth or sixth moult the little lobsters sink to the bottom,and then begin their journey shoreward. From this timeuntil they are about four inches long, only very few indi-viduals have ever been seen. This is due, it is said, tothe fact that they hide deep down among the rocks, wherethey cannot be dredged. When they are four inches longor so, they become bolder, leave the rocks, and, like the. FIG. 115. — Larval view of lobster, extracted from anegg which was about ready to hatch. The concretionsin the intestine are destined to go into the newcuticulaafter moulting, x 25. From Herrick. adults, make burrows for themselves in the sand or understones. Development of Crayfish. — The crayfish develops simi-larly to the lobster, — from a large egg filled with early stages are much like those of the lobster; butthose changes which in the lobster take place during thefirst three stages of free life are in the crayfish passed inthe egg. Consequently at the time the crayfish hatches it 118 ZOOLOGY is almost, but not exactly, like an adult crayfish exceptin size. The telson of the just-hatched crayfish has, to beprecise, a somewhat more oval form, and the first pair ofswimmerets are undeveloped; but these differences soondisappear.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1900
