Zoology. — “On the larval development of Oxyuris equi (Schrank)”. 
By J. HE. W. Inte and G. J. van Oorpr. (Communicated by 
Prof. SLuIrEr.) 
(Communicated at the meeting of May 29, 1920). 
The only treatise known to us‘) on the larval development of 
Oxyuris equi is the one by Rainumr and Henry (1903). In this 
article two different forms of larvae are described: 1. those, having 
a length of about 5—10.5 mm. and 2. those measuring 5—6 mm. 
The posterior extremity of the body differs in these two forms. In 
the former the anus is situated rather far from the posterior extre- 
mity, in the latter this distance is shorter. In neither forms gonads 
are formed as yet. 
On the ground of the above and also because the second form 
occurs less often, Rainier and Henry are of the opinion that the 
former represent female, the latter male larvae. In certain characters 
(the presence of cuticular rings, of rectal glands and of rectal muscles) 
they correspond to adult Oxyuris-specimens, in many others they 
differ. Both larval and adult Ozyuris live free in the colon and 
coecum of the horse. The larva found by the French authors “parait 
être simplement une forme larvaire de |’Oxyuris equi (Schrank), ou 
“mieux une forme immature, qu'une dernière mue doit amener a la 
forme adulte” (RaiLrier et Henry 1903, p. 137). When the number 
of moults of Oryuris corresponds to that of many other Nematodes, 
this is the fourth and latest moult, according to the investigations 
of Surat (1914). 
In the material, collected by the commission, charged with the 
Sclerostomiasis-inquiry in Holland, we found the larval forms, 
described by Raimrter and Henry in many specimens, taken from 
different horses. In order to judge of the correctness of the opinion 
of the French authors, holding that the imaginal Oxyuris originates 
from this larval form by a last moult, we had to look for moulting 
specimens in the first place. We succeeded in finding a good number 
of such specimens, and so we could make out with certainty that 
1) PerRoncito’s article: “Sviluppo degli Oxyuridi’, Giorn. Acc. Med. Torino. 
Vol. 6, 1903, was not seen by us. 
