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 

 larvae that issue from the ova are 300 fi long and 95 fi 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 (A teles) ; 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 



