330 ECONOMIC IMPORTANCE OF NEMATODES. 



Oesophaf/o.stoinuin stephauostomuiii lias been 

 recorded from submucosal liaemorrliagic cysts in the 

 human intestine. 



Ancylostonia duodenale. — The " miner' s-worm," 

 or " hook-worm." Inhabits the small intestine, chiefly 

 the jejunum, and causes pernicious anaemia. Its occur- 

 rence is world-wide. 



A. ceylanicum, and A. hraziliense are allied forms. 



Necator americanvs. — This parasite was formerly 

 confused with Ancylostonia duodenale ^ and its action is 

 similar. 1+'^ distribution is also wide. 



ascahidae. 



Ascaris lit mhiico ides. — This parasite, popularly 

 known as the " round " worm, is one of the most 

 frequent parasites of man, in the intestines of whom 

 they often occur in large numbers. It is universal in its 

 distribution. 



OXYURIDAE. 



O.vyun's vermicidaris. — The common " seat-worm," 

 inhabits the large intestine. The young- fonns are 

 frequently found in the vermiform appendix, and 

 latterly a role has been suggested or assigned to them 

 in the cause of appendicitis. 



lY. — Some Remarks on the Life-History of Heterodera 

 IN South Africa. 



The life-history of Heterodera radicicola may perhaps be 

 treated more extensively, as it merits observation both on 

 account of the peculiarities of its development and because 

 of the practical interest that must be attached to one of the 

 most destiiictive and, at the same time, one of the most 

 uncontrollable of plant parasites. The genus has been the 

 subject of investigation by the author of this paper for a 

 considerable time past, and the following is a brief resume 

 of its development, together with some observations on the 

 biology of the parasite, which, it is hoped, may help to 

 elucidate the numerous difficulties and problems that have 

 arisen . 



On cutting (i])en the " gall " or " knot " of a root 

 infested with Heterodera, a variable number of pearly white 

 pear-shaped " cysts " about 0*7 mm. in length are visible. 

 These " cysts " prove to be the adult gravid females of the 

 parasite, which have become swollen on account of the large 

 numbers of eggs within the body, and it is to iiTitation of the 

 root tissues set up bv their presence that the lapid multi- 

 plication of cells, leading eventually to the formation of root 

 galls, is due. In the parasite, presumably H. radicicola , 

 common througliout vSouth Africa, that has been investigated, 

 the eggs, sixty to eighty in number, undergo segmentation, 

 and the larvae emerge from the e^^ cases while still within 

 the uterus of the now defunct mother. Despite careful 



