136 NEW YORK ZOOLOGICAL SOCIETY. 
heat and moisture. The period occupied in this development va- 
ries according to the environment, but on incubating in water at 
a suitable temperature an embryo soon becomes visible in their 
interior, and hatching is completed in two or three days. The 
larvee that issue from the ova are 300 mw long and 95 p broad; 
their posterior extremity is elongated into a tapering tail; in de- 
veloping they moult two or three times, and attain adult con- 
dition after passing with the water into the intestines of their 
host, without requiring an intermediate host. Eight days after 
this passive migration they are 5 mm. to 1 mm. long, and in cer- 
tain details resemble the definite form. On the tenth day the old 
chitinous integument is shed, the buccal capsule appears, and it 
is only now that the group to which the parasite belongs is recog- 
nizable. It retains this form for three or four days, during which 
it acquires its final dimensions, and a second moulting results in 
the parasite acquiring its sexual individuality. 
These details, and particularly the essential part that water 
plays in the evolution of this parasite, show that infestation prob- 
ably takes place through the medium of the drinking water, and 
that the hosts contaminate each other by scattering the ova of 
their parasites in the water-troughs. This shows the necessity 
of having elevated drinking places, so as to reduce the infection 
of animals from this source to a minimum. 
The genus Filaria is a very large and important one. Like 
Ascaris, it is confined to Vertebrates, but usually lives in the tis- 
sues of the body and not in the intestines. Several rare members 
of this genus have been found among the Park animals. 
Filaria gracilis (Rudolphi).—Fourteen specimens of this nema- 
tode were found in a spider monkey (Ateles) ; one of this num- 
ber was partially encysted in a false sac formed by the costal 
pleura. Two more were quite firmly adherent to the pulmonary 
pleura on the left side. Seven or eight were found in the abdomi- 
nal cavity, five of which were situated between the folds of the 
mesentery of the small intestines. One was found coiled around 
the portal vein, while several were found in the mesenteric blood 
vessels. Owing to the extreme rarity and great length of this 
nematode, I think it is of sufficient interest to warrant a short 
description. 
Prior to this writing I am not aware that this worm has ever 
been found in this country. However, a number of preparations 
of this Filaria are reported to be in the Museum of the Royal Col- 
lege of Surgeons in London. Some of these specimens were 
originally obtained by Professor Owen from the pleural cavity 
