. Animal biology. Zoology; Biology. PHYLUM NEMATHELMINTHES 181 A/foufh Pharynx A/erve ce//s A/erve Ccru^/cff /r7¥^es-/^/rte absorption through the thin wall of the intestine into the body cavity. By means of this cavity it is distributed throughout the body. Within tissues it is passed from cell to cell. Egestion takes place through the anal opening and elimination is effected by the excretory system. 211. Reproduction.—The nemathelminths are all diecious, and ferti- lization is internal. After fertilization those eggs which develop within the body, as in the species of Trichinella, are lodged
. Animal biology. Zoology; Biology. PHYLUM NEMATHELMINTHES 181 A/foufh Pharynx A/erve ce//s A/erve Ccru^/cff /r7¥^es-/^/rte absorption through the thin wall of the intestine into the body cavity. By means of this cavity it is distributed throughout the body. Within tissues it is passed from cell to cell. Egestion takes place through the anal opening and elimination is effected by the excretory system. 211. Reproduction.—The nemathelminths are all diecious, and ferti- lization is internal. After fertilization those eggs which develop within the body, as in the species of Trichinella, are lodged in the uterus, where they hatch, the female bringing forth living young. The shell is often heavy and very resistant to chemi- cals which would inj ure the organ- ism. The larva, which at first may be free and may remain so in free- living nematodes, enters, in the case of all parasitic forms, into another animal which may be either an intermediate or a final host, or into some plant. 212. Life History of the Pig Ascaris.—The parasitic nematodes S^^^"^ possess some very interesting and remarkable life histories. One of these is that of the ascaris found in the pig. The adult pigs are immune from infection by this parasite, which, if it is found in a mature pig, must have entered it when the host was young. The eggs of the parasite, after being passed out with the feces and mixed with the soil in the hog ^j^ ^i.—UonhysUra sentiens Cobb, a lot, are taken up by the young pigs free-living nematode. Side view of female. ,, 1 • , 4. u i. Probably the most widely spread nematode as soon as they begm to root about; g^^^^^^ ^^^^^ -^ ^^.^^^^ ^ater, in the sea, and in or if infested soil is caked upon soil. (From Cobb, in Ward and Whipple's ,, , 1 ~ ., ,, ,, "Fresh-water Biology," by the courtesy of John the body of the mother, the eggs j^^^^y ^ sons. inc.) x 94. may be taken in when suckling. The eggs pass into the intestine of the young pig and by the destructio
Size: 1188px × 2103px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcoll, booksubjectbiology, booksubjectzoology
