EXPLANATION OF THE PLATES. 1>M 



Plate V.— Altehnation in the Extozoa, <kc. 



Figs. 1-3 illustrate tlio successive pliasos in the dovolopim-ut 

 of the Tapeworm— (pp. 9G, 131, IGl). 



Fig. 1.— The egg of a species of Tapewonji, T(rtn4i PUtHlum, 

 (from Dujardiij), \\ith its six-hooked contractile enil)r}'o. 



Fig. 2. — The Cysticenis (from Bremser), now known to l>e tlu- 

 cystic phase of the Tcenia Solium ; a the head, formed originiilly 

 within the cyst b, and then extruded by the evagination of it« 

 hollow pedicle or neck. In tlie farther development within the 

 alimentary canal, the cyst is throwai off, and the neck extended, 

 by the gemmation and multipHcation of its joints, into the long 

 body of the Tapeworm. 



Fig. 3. — Ultimate development of the Tttnia risfillnm of the 

 Shrew (from Dujardin) — a, the head ; b, the neck, formed of un- 

 developed segments ; c, the body, formed of segments which 

 iiave acquired their full size, and become filled with ova. 



Figs. 4-7 illustrate the development of the Echhiococcus ur 

 Hydatid— (p. 131). 



Fig. 4. — A diagram of the simple Hydatid cyst — (EchiiU)CoccHs 

 scolicipariens) — the first result of the transformation of the con- 

 tractile vesicle discharged from the egg of a minute species of 

 TcBnia. Derivative Taenia-buds are represented in the course of 

 development from the interior of the cyst — (p. 131). 



Fig. 5. — A diagram of the compound Hydatid {Echiiwcoccuif 

 altricipariens)^ resulting from the intermediate gemmation of 

 secondary cysts, prior to the formation of proper Tfenia-buds. 



Fig. 6. — A Tsenia-bud, with its denticulated head a in proce.';s 

 of development, on an invagination of the wall of the cystic poi-- 

 tion b ; c pedicle of attachment to the parent cyst. 



Fig. 7. — A fully-formed Tsenia-bud, with its head everted 

 (both from Wilson). 



Figs. 8-11 (mostly from Steenstrup) illustrate the successive 

 forms in the alternation of the Trematoda — (pp. 95, 112). 



Fig. 8. — Egg of Mo'Tiostomiim mutabile (from Siebold) with its 

 infusorian embryo. 



Fig. 9. — Redia or intermediate form of Distoma, derived from 

 the infusorian, and forming in its owii interior an agamic brood of 



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