STRONGYLOIDES STERCOKALIS 



The females of the free-living 

 generation (rhabditiform) deposit from 

 thirty to forty eggs, which develop 

 rapidly, sometimes even within the 

 uterus in the case of old females. 

 After the larvae have emerged from the 

 egg-shell, they measure 0^22 mm. in 

 length, and possess the characteristics 

 of the parents (rhabditiform larvae). 

 When they have grown to 0-55 mm. 

 they moult, and while losing their 

 own characteristics they acquire the 

 characteristics of their parasitic grand- 

 parents (strongyloid or filariform). 

 After about eight days the free-living 

 adult generation in the cultures have 

 disappeared, and all the rhabditiform 

 larvae have been transformed into 

 strongyloid or filariform larvae ; they 

 then die off unless they reach the 

 intestine. 



This cycle of development holds 

 good for Strongyloides stercoralis of 

 tropical origin (Bavay, Leuckart, Leich- 

 tenstern, Zinn). In the European 

 Strongyloides the free-living genera- 

 tion, as a rule, is absent (Grassi, 

 Sonsino, Leichtenstern, Braun) ; the 

 rhabditis-like larvae evacuated with the 

 faeces are transformed into the strongy- 

 loid or filariform type of larva (in 

 cultures which are easily made) which 

 will only become adult if introduced 

 into man. 



So that we have these two cycles : 

 (A) (i) $ parasitic, (2) eggs, the rhab- 

 ditiform larvae in faeces, (3) free- 

 living strongyloid or filariform larva, 



(4) ? parasitic. (B) (i) (2) (3) as before, 

 then (4) adult ? and $ , free living, 



(5) eggs, (6) rhabditiform larva, 



(7) strongyloid or filariform larva, 



(8) $ parasitic. 



Infection of man results not only 



Nerve-ring 



Subventral ceso- 

 phageal glands 



Excretory pore 



CEsophagus 



~- Genital rudiment 



Anus - 



FIG. 274. Strongyloides stercoralis: 

 mature filariform larva showing long 

 transparent oesophagus, slender granu- 

 lar intestine and characteristic tip to 

 the tail ending in two small points, 

 x 620. (After Looss). 



