STRONGYLOIDES INTESTINALIS 



279 



that size, until they are' passed out with the faeces. They already 

 differ from the parent in the shape in the oesophagus. When 

 the external temperature is sufficiently high (26 to 35 C.), they 

 become mature after moulting. 

 In about thirty hours they are 

 completely developed and co- 

 pulate. At a low tempera- 

 ture they certainly cast their 

 skin, but do not escape from 

 the old cuticle and do not 

 develop further. At a tem- 

 perature of about 25 C. only 

 some of the larvae attain 

 maturity. 



Every female of the free- 

 living generation deposits from 

 thirty to forty eggs, which 

 develop rapidly, sometimes 

 even within the uterus. After 

 the young have emerged from 

 the egg - shell, they measure 

 0*22 mm. in length, and possess 

 the characteristics of the pa- 

 rents (rhabditis form). When 

 they have grown to 0*55 mm. 

 they moult, and while losing 

 their own characteristics they 

 acquire the characteristics of 

 their grandparents (Strongy- 

 loid or Filariform larvae). After 

 about eight days the free-living 

 adult generation in the cul- 

 tures has disappeared, and all 

 the young have been trans- 

 formed into the Strongyloid 

 form ; they then die off unless 

 they reach the intestine. 



This cycle of development holds good for Strongyloides intesii- 

 nalis of tropical origin (Bavay, Leuckart, Leichtenstern, Zinn). In 

 the European Strongyloides the free-living generation, as a rule, 

 is absent (Grassi, Sonsino, Leichtenstern, Braun) ; the rhabditis- 

 like larvae evacuated with the faeces are transformed into the 



FIG. iQ2. Strongyloides intcstinalis. 

 On the left above a larva from the faeces ; 

 under it a male of the free-living genera- 

 tion, on the right a female. Magnified. 

 (After Zinn.) 



