* He tieu hod
6 cac nhom ky sinh khac nhau, he tieu hoa co su bien doi theo hai hudng khac nhau: - Hudng thur nhat la ruot phan nhanh nhieu hon va phinh rdng hon de chura luong thuc an nhieu hon. Ddi vdi cac vat ky sinh dinh dudng bang mau con phat trien cac tuyen chong dong mau (giun moc, dia, giun xoan da mui khe).
- Hudng thur hai la tieu giam ruot va chuyen sang dinh dudng tren toan bo be mat co the. VI du nhu d san day, giun dau gai, nguyen sinh d6ng vat (Astomata), giap xac
(Sacculina) (hinh 22)....
Hinh 22. Giap xac Sacculina ky sinh a dudi bung cua
* He than kinh vd ca quan cam giac
Doi voi noi ky sinh, xu hudng chung la tieu giam mot sd co quan (vf du nhu mdt). 6 au trung Cercaria sdng tu do trong nude co mot mdt (hinh 23) dd tim vat chu trung gian, con d san la trudng thanh mdt hoan toan tieu giam. 6 ngoai ky sinh trung khong thd hien
Hinh 23. Cercaria co mdt
A - Cercaria Notocotylus; B - C it ngang Cercaria Notocotylus ngang Cercaria Notocotylus
1 - Mat; 2 - Ong bai tiet; 3 - Nhanh ruot; 4 - Hach nao; 5 - Thifc quan ruot; 4 - Hach nao; 5 - Thifc quan
He bai tiet d vat ky sinh khong the hien bien doi g] dac trung. Mot so trudng hop, he bai tiet co tieu giam mot phdn. Vf du, d nguyen sinh dong vat Sporozoa co sir tieu giam khong bao.
* He ho hap
Ddi vdi ngoai ky sinh trung khong co gi thay doi so vdi dong vat sdng tu do. Ddi vdi noi ky sinh trung, gdn day ngudi ta da chung minh duoc rdng ky sinh trung phai trai qua qua trinh len men ky khf va ua khf lien quan den viec su dung oxy tu do, kieu h6n h(^> do ngudi ta goi la ky khf tuy tien. Trong co the vat ky sinh ky khf co lugfng glycogen du tru ldn, day la nguon nang luong chu yeu cua chung. Ngoai ra, trong mo vat ky sinh con co sd luong md ldn, md la san pham cuoi cung cua qua trinh len men glycogen.
* C a quan van dong
Co quan van dong cua ky sinh ft nhieu co sir tieu giam. Vf du, a giun nhidu to ky sinh (Myzostomida) chan tieu giam nhieu so vdi nhung loai cung giong sdng tu do; d
Copepoda tieu giam chan; d ve, ran mat canh v.v....
* He sinh due
Chuc nang sinh san ddi vdi phan ldn vat ky sinh la rat quan trong. Do ddi sdng ky sinh, cac ca the due va cai rat kho gap nhau, vi vay nhieu vat ky sinh co xu the ludng tfnh. Vf du: san la, san day.
Trong s6 san la ho Didymozoonidae ky sinh d duori da hoac a mang, xoang mieng
theo chieu hudng ph£ln tinh thanh con due va con cai (hinh 24).
A - Con dire va con cai trong cung mot nang;B - Con cai; C - Con difc B - Con cai; C - Con difc
1 - Lo mieng; 2 - Giac mieng; 3 - Ong d in tinh; 4- Nhanh ruot; 5 - TCr cung; - Nhanh ruot; 5 - TCr cung;
6 - Tinh hoan; 7 - He sinh due tieu giam
khi con cai duoc giu trong mang cua con due. Giun tron Syngamus phan tinh (hinh 25) sdng trong khi quan gia cim va chim, con due trong sudt, bam chat vao co the con cai d vung 16 sinh due cai. Con due be, con cai ldn va bao gid cung cap doi.
Tang sd luong san phdm sinh due la su thich nghi
qua trinh phat trien. Vi du: giun bao Trichinella spiralis tuy kich thudc nho nhung de den 10.000 a'u trung. Giun moc trong 1 ngay dem de 20.000 trung, mat khac ddi sdng cua chung keo dai tdi 4 - 5 nam. Giun dua trudng thanh sdng 5 - 6 thang, m6i ngay de 200.000 - 250.000 trung. San la ruot Fasciolopsis buski m6i ngay de 25.000 trung. Tang sd luong co quan sinh due d m6i dot lam cho kha nang sinh san cua vat ky sinh tang len gap boi (Vi du: Cestoda) (hinh
cua ca bien, thudng gap ca hai ca the trong cung mot nang, mac du ludng tinh nhung hai ca the nay khac nhau ve kich thudc va kha nang de triing, nghia la chung dang phat trien
Hinh 24. San la Wedlia bipartita (Didymozoonidae)
cua vat ky sinh vdi ddi sdng ky sinh de bao toan noi giong, chong lai cac dieu kien khong thuan loi trong
26).
Hinh 25. Giun trdn Syngamus (due va cai)
Con di/c be bam chat vao co the con cai 6 vung lo sinh due
Hinh 26. Dot san day vdi 2 co quan sinh due
A - Diplogonoporus grandis(Pseudophyllidea)-, B - Moniezia (Pseudophyllidea)-, B - Moniezia
expansa (Cyclophyllidea)-, C - Dipylidium caninum
(Cyclophyllidea)
1 - Cd quan giao phoi; 2 - Am mon;3 - Buong trCfng; 4 - Tinh hoan; 3 - Buong trCfng; 4 - Tinh hoan; 5 - Tuyen gian dot; 6 - Tuyen noan
hoang
Hinh thai trung cua vat ky sinh cung phat trien theo chiSu hudng da dang. Su thfch nghi ve hinh thai cua trung giup cho chung phat tan tot hon. Vf du: trirng cua nhieu loai san day va san la don chu co rau dai, hoac nhon (hinh 27, 28); san la mau co gai nhon de pha thanh mach vao ruot.
Hinh 27. Triftig cua cac loai san la don chu (Monogenea)
A - Diplectanum aculeatum; B - Mazocraes alosae; C - Benedenia derzhavini;D, H - Microcotyle gotoi; E - Acanthocotyle verrilli; F - Protoancyrocephalus strelkowi; D, H - Microcotyle gotoi; E - Acanthocotyle verrilli; F - Protoancyrocephalus strelkowi;
Hinh 28. Trimg san day (Cestoda)
A - Trimg Amnomotaenia platyrhyncha;
B - Trimg A. paramicrorhyncha
1.3.5. Thich nghi phoi vd cac giai doan du triing
Cac giai doan phat trien phoi d phdn ldn vat ky sinh khong co gi sai khac so vcri cac dang song tu do g£tn gui chung. Dieu do giai thfch rang, hiu het trimg phat trien d mdi truong ngoai khong chiu anh hucmg ciia phfa vat chu. Vf du, su phat tri£n cua trung giun dua khdng sai khac sir phat trien cua trung giun tron song tu do. Tuy nhien, mot so' trudng hop su phat trien cua phoi cd lien quan chat che vdi vat chu, dinh dudng nhd vat chu. Ngudi ta nhan tha'y d chung cd cac mure do thfch nghi khac nhau. Vf du, a'u trung cdn trung khdng phan dot, thieu chan, he than kinh, he hd ha'p va he co phat tridn chua ddy du, chu yeu phat trien he tieu hoa.
Mot sd vat ky sinh khac cd co quan chuyen hoa thfch nghi vdi ddi sdng ky sinh. Vf du, dudi a'u trung Cercaria cua mot sd loai san la mau che ddi hoac cd mang bai.... giup
Cercaria bai sau vao nude de tiep xuc vdi ca, sau dd bam vao da ca va mang ca, xam nhap vao mach mau. Hoac d mot sd khac (Azygia) cd dudi to va cd tui de ca mang dd nhan biet, tui giup a'u trung bao ve khi bi ca mang nuot phai (hinh 29).
Cac dang a'u trung hoac cac giai doan phat trien sdm cua vat ky sinh cdn chung minh duoc nguon goc t6 tien cua chung. Vf du, giai doan au trung Miracidium d san la va Coracidia a san day co the deu cd phu tiem mao, chung xua't than tu to tien song tu do la Turbelleria.
Hinh 29. Au trung Cercaria cua cac loai san la - Trematoda
A - Cercaria Sanguinicola cd the co mang bdi bdi
B - Cercaria Azygia co tui