504 The Philippine Journal of Science im 



worm or of Strongyloides, the latter of which are frequently 

 numerous in the same culture of monkey's faeces. The newly 

 hatched oesophagostomum larva is characterized: first, by an 

 extremely long filiform tail and, secondly, by the zigzag course 

 of the intestine which is plainly visible in the living worm. 

 These tv/o characteristics are well represented in Plate I, fig. 3, 

 and Plate II, fig. 2. 



The small rhabditiform larva grows rapidly, and under favor- 

 able conditions of culture and temperature attains its maturity 

 in from three to four days. In the process of growth it molts 

 twice. At the last molt the old skin is not shed, but remains as 

 a sheath inclosing the larva. Within the sheath the larva con- 

 tracts somewhat in breadth and more in length, so that it is 

 separated from the old larval skin by a considerable space. The 

 larva no longer possesses the long filiform tail, which was present 

 up to the last molt, as is seen from the inclosing larval skin 

 (Plate III, fig. 1). The character of the oesophagus has also 

 changed during the last molt from the rhabditiform to the 

 strongyliform (compare Plate II, fig. 1, with Plate IV, fig. 1). 

 This larva inclosed in the skin of the last molt remains alive 

 and active, but undergoes no further development in the cul- 

 ture. It is the mature larva ready to infect a new host. It 

 diff'ers from the mature larva of the hookworms and strongy- 

 loides in size and shape, and especialy in the long filiform tail 

 of the old larval skin inclosing the worm. The mature larva is 

 about 0.9 millimeter long and 0.03 millimeter thick. 



The larval development of (Esophagostomum apiostomum, 

 therefore, is strikingly similar and wholly comparable with the 

 development of Ankylostoma duodenale, which is perhaps to be 

 expected from the somewhat near relationship of the two worms. 

 From this similarity in the development of the larva, one would 

 expect by analogy that the method of entrance of the larva into 

 the body of the host would also be similar. It has been demon- 

 strated by Looss (1911), and substantiated by other investi- 

 gators, that infection with ankylostoma larvae may take place not 

 only by ingestion, but also by passage through the moistened skin. 

 This is supposed to take place especially in case of persons going 

 about barefooted. The larvae enter the follicles and attain the 

 blood vessels, by which they are carried to the lungs. Here they 

 leave the blood and enter the air vesicles and then travel by the 

 way of the bronchi, trachea, oesophagus, and stomach to the in- 

 testine. The method by which the larva of oesophagostomum 

 enters the body of its host and attains its position in the tissues 

 of the large intestine is now being experimentally investigated. 



