98 JOURNAL OF THE 



pursuing for a time a wandering life undergo a metaniorphosisf 

 accompanied by what a[)pears to be a retrogression, so that the 

 creatures lack the power of h)comotion. At the third moult of 

 the male it is transformed again into a more highly organized 

 being, possessing wings and capable of seeking its mate. On 

 the other hand, the female remains fixed and incapable of loco- 

 motion, and after impregnation by the male becomes enormously 

 distended with eggs. It mu.^t be borne in mind, however, that 

 this anah)gy is only superficial. Heterodera does n or lose its 

 power of locomotion through any retrogression of form like the 

 loss of organs which occurs in the Cjcc/yfc, though, according to 

 Strubelljsome parts of the ht^al un lergo retrogression. It is 

 because of the rigidity and distension of the bidy of b.)tli male 

 and female so that it cannot perform the undulatory movements 

 of the body by which locoujotion in the larval state and in the 

 adult male is acconiplished. The fact that the cyst is surrounded 

 by the tissues of the plant does not interfere with its independ- 

 ent l»)Comotion. 



The cystj; differs mor[)hologically from that o^ Xematodes like 

 Trichina, where the larva becomes encysted in the muscles of its 

 host and does not underjxo anv remarkable change of form in the 

 formation of the cyst, the walls of which are formed from extra- 

 neous and excreted matter. It son)ewhat resembles in its origin 

 and earlier sta;i:es the earlier staj^es of certain of the Cestodes like 

 Tcenia,^ where the embryo after it is located in the tissues of its 

 host develops by distension into a vesicular body. Here, how- 

 ever, the resemblance ceases, and the walls of the T(rnia cyst by 

 invagination or evagination produce the head of thi' worm, or 



ftiis dem Gesammt^^ebiete der Zoologie, hrsg., von R. Leiickfirt «. C. Clnm. Heft 2) 4° 50 

 pg. 2 Taf. Cassel (Th. Fischer) 1888. 



<'entralblatt fur Bakteriologie und Parasiteiikunde. Bd. VI, No. 15, pp. 421-420, Jena, 

 188!». 



Muller, Mittheilnngen nber unseren Knlturpflanzen snhadliclip, das (re-'^chlecht Hete- 

 rodera hildcnden Wiiimer. I.andwirtliseliaftliflie Jahrbiiolier, Bd. XIII, Heft 1,1884. 



Soraner, PHanzPiikranklieiten, Zweito .Aiitlatre, Kr.^^ter Banil, pp. 852-85», 1880. 



Stiubell, Ad. I'^eber den Ban nnd (iie Entwickelung von Heterodera Sehachtii Selimidt- 

 Zoolog. Anzeiger, No. 242, 17, Jannar, 1887., pp. 42-4(;, nnd No. 24:5, .11, Jannar, 1887, pp- 

 (i2-<;(;. 



Centralblatt fnr BakteriiJogie nnd Parasitenknndo. Band I, pp. G0.3-C04, Jena, 1887. 



tConi.^tock — \i\ Introduction to Entomology, Itliaca, N. Y., 1888. 

 Ann, Kept. U. S. Dept. Agr., 1880. 



JMy use of the term cyst is mainly for convenience. 



^Text-book of Zoology, Clau.s and Sedgwick. 



