Zöology; a textbook for colleges and universities . e-banded armadillo of Texas poly-embryony regularly occurs, four individuals being pro-duced by a fertilized egg cell. These, as in the case ofidentical twins, are always of the same sex and very THE INDIVIDUAL 39 much alike. They differ to the same extent that thetwo sides of any single individual may differ. c. The question of the individual may be discussed Processes J •of regenera- from another standpoint. When we accidentally knock tion afteroff a small piece of skin, the wound heals; but if we mjuilose a finger, no new finger grows in i
Zöology; a textbook for colleges and universities . e-banded armadillo of Texas poly-embryony regularly occurs, four individuals being pro-duced by a fertilized egg cell. These, as in the case ofidentical twins, are always of the same sex and very THE INDIVIDUAL 39 much alike. They differ to the same extent that thetwo sides of any single individual may differ. c. The question of the individual may be discussed Processes J •of regenera- from another standpoint. When we accidentally knock tion afteroff a small piece of skin, the wound heals; but if we mjuilose a finger, no new finger grows in its place. A lizard,however, may lose its tail, and a new tail grows. If thetail is broken at one side, sometimes a tail begins togrow at the point of fracture, and two tails to a lower level in the scale of animal life, wefind that the arm of a starfish, removed with a certainamount of the disk, will grow new arms and eventuallyform a whole starfish. Many of the lower invertebratesmay be divided into two or more parts, and each part. FIG. 9. Renilla, a compound animal, living in the sea(Phylum Ccelenterata, Order Alcyonaria). will regenerate what it lacks, producing a whole in-dividual. This is not the division of ordinary reproduc- 4o ZOOLOGY Colonies ofpolyps Humanpersonality tion, not even a normal budding process, but a violenttearing apart of the individual, the parts of which con-tinue to function nevertheless. A man cannot be sotreated, and survive; but there is every transition be-tween the process of healing in a wound and that ofcomplete regeneration of two individuals upon division. 6. The individual is elusive also in those lower formsof life which exist in groups or colonies, such as thezoophytes or hydroid polyps. These animals occur innumbers on a common stem, through which nourish-ment passes. On account of this arrangement it ispossible for the individuals to assume very specialfunctions, some for feeding, some for defense, others forreproductio
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1920
