Identifier: introductiontozo00dave Title: Introduction to zoology; a guide to the study of animals, for the use of secondary schools; Year: 1900 (1900s) Authors: Davenport, Charles Benedict, 1866-1944 Davenport, Gertrude Anna Crotty, 1866- Subjects: Zoology Publisher: New York, Macmillan company London, Macmillian and co., ltd. Contributing Library: MBLWHOI Library Digitizing Sponsor: MBLWHOI Library

View Book Page: Book Viewer About This Book: Catalog Entry View All Images: All Images From Book

Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image: 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 yolk.The 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.

Text Appearing After Image: FiG.lloa.—Third larval stage,lateral view. Note the dif-ference between this andthe adult. X 11. FromHerrick. Regeneration of Lost Parts. - -If you attempt to pick upa crab by one of its claws, you frequently find yourself inpossession of a portion of the leg only, while the crustaceanhas made good its escape. Moreover, it will be seen thatthe leg always separates at a certain place ; namel}r, be-tween the second and third segments. This is the placewhere a fusion occurs between two segments which are free TIIE CRAYFISH AND ITS ALLIES 119 in the first larval stage. This power of defensive mutila-tion occurs in those appendages which are most apt to beseized,—namely, the five thoracic legs, — and is whollyunder the control of the reflex nervous system, for it mayoccur when the entire voluntary nervous system has beenremoved. The leg of a dead crustacean shows no suchcapacity. If the leg of a lobster is cut off at some pointdistal to that of normal rupture, the limb will later bef

Note About Images