BY N. A. COBB. 173 



is the view generally obtained under the microscope, it presents a 

 nearly straight ventral and a decidedly arcuate dorsal contour, 

 the anterior end being evident from its pointedness. At the 

 anterior end, then, and on the dorsal surface of the shell of the 

 egg of Oxyuris vermicular is is a circular area whose 

 structure is not uniform with that of the remainder of the shell, 

 and which is destined to give way for the passage of the embryo 

 on its issuing from the egg (PI. viii, Fig. 1). Now that I have 

 demonstrated its existence I have no difficulty in seeing this 

 structure at any stage after the formation of the sliell, though 

 through the action of the gastric fluids it very soon becomes much 

 more apparent as a porous area. Whether the pores exist pre- 

 vious to the action of the gastric fluid or are a result of its action 

 I cannot positively state. I believe, however, that something like 

 the former is the case and that the porosity becomes more 

 apparent as the stomach fluids continue to dissolve this part of 

 the shell, which ultimately becomes so weak that the movements 

 of the embryo cause it to give way. 



The embryo seems to issue uniformly tail first.*' A fully 

 formed embryo is doubled upon itself twice, the posterior bend 

 being situated at the anterior end of the egg. It is this pos- 

 terior bend that issues first, followed by the tail, and finally the 

 head. 



Wliether the above described area will be found to bear any 

 relation to the ovarian history of the eggs and the entrance of 

 the spermatozoa remains to be seen. It seems to me not im- 

 probable that a connection may exist. 



Experiment III. 

 All the numerous eggs used in this experiment contained fully 

 developed embryos, nearly all of which became hatched inside of 

 six hours, proof enough that quick advantage is taken by 

 Oxyuris vermicularis of a cliance to establish itself in 

 the human alimentary canal. A goodly amount of gastric fluid 

 entered the capsule, and the results must be regarded as quite 

 * I speak here from later observations. 



