610 
pore and anterior extremity is 2.45 mm., a vagina is not yet visible. 
The moulted worm. 
The moulted immature Oryuris agrees in all respects with adult, 
full-grown specimens and is at once distinguishable from the larval 
form by the possession of a long stretched pharynx. Fig. 5 shows 
us a moulted, but not yet full-grown specimen, having a length of 
9.2 mm. (catch N°. 42). The hexagonal mouth-opening opens into 
a small mouth-cavity. In this cavity three obtuse teeth are visible, 
situated in the three sectors of the corpus pharyngis. Behind these 
teeth lies a circle of very pointed bristles. In fig. 5 these three teeth 
and the optical section of the bristle-circle are indicated. The corpus 
pharyngis gradually passes over into the isthmus, which is much 
narrower, this isthmus again into the bulbus, which is about equally 
thick as the corpus. The pharyngeal lumen is much narrowed and 
(ri-radiate in transverse section, as is also the case in the larval 
form. The posterior extremity of the bulbus also possesses three 
valves protruding into the lumen of the intestine. An oesophagus in 
Martini’s sense is not visible. The pharynx of ¢ and ¢ shows no 
differences. 
The moult. 
How does the pharynx of the form, just described, originate out 
of that of the larva (fig. 3)? Numerous moulting specimens enabled us 
to trace this and we could study the prolongation of the pharynx 
in particular. Moulting specimens can be at once recognized by the 
fact that beneath the old cuticle of which the rings are of a con- 
siderable breadth (60—75 u), the new cuticle with very narrow 
rings (+ 12 u) is visible. 
In specimens, on the very first act of moulting, the larval pharynx 
is still present without change. Then the part of the bulbus, lying 
immediately behind the corpus lengthens markedly, and forms the 
isthmus in this way. Originally the lateral cells lie to the left and 
to the right of the bulbus. During the lengthening of the bulbus 
they remain in their place. The corpus too lengthens a little, but not 
so markedly as the bulbus; and so the lateral cells come to lie near 
the transition of corpus and isthmus in moulted specimens (fig. 5). 
We possess a preparation of a stage, in which the longitudinal 
growth of the bulbus has just started, but where the corpus still 
has the larval shape. The first anlage of the isthmus has been formed 
already. So the corpus lengthens later than the bulbus, through the 
outgrowth of which the isthmus is probably wholly formed. The 
prolongation of the pharynx takes place quickly: the different stages, 
mentioned above, occur in specimens of about the same size. 
