Two Neiv Species of Chaetor/asfer. 80 



can ascertain there has been no species of Ciutetogaster hitherto 

 recorded from Australia. During last year I found some of the 

 pond snails I was keeping in vessels infested with this small para- 

 site. These snails came originally from Merri Creek, Weeweerup, 

 Yackandandah, and Geelong; and it is probable that the parasite 

 also came from these several localities, as there does not seem to 

 have been any possibility of infection between the separate jars. 

 On examination there were found to be two species present. In 

 most of the jars there was the form I shall describe as Chaetoga^ter 

 australis, and this was present in very great numbers; but in one 

 jar (from Merri Creek), and also on some snails in a pond in the 

 University grounds, parasitic on a species of Isidora (I. texturata), 

 "were a few specimens of a much large species, which I shall describe 

 as Chaetogaster victoriensis. 



A great deal of the structure of Chaetogaster can be made out 

 by examining the living animal, as it is very transparent. I also 

 worked with sections, both transverse and longitudinal, and with 

 preserved animals, stained and mounted whole. Chaetogaster is 

 very difficult to kill satisfactorily, as it contracts rapidly and disin- 

 tegrates very readily. The method I found most successful was to 

 kill the animal by pouring on to it boiling 70 per cent, absolute 

 alcohol. This acts as a fixing and preserving agent. I used several 

 different stains ; the most satisfactory were methyl blue for staining 

 whilst alive, borax carmine for the specimens mounted whole, and 

 acetic acid alum carmine for the sections. 



Chaetogaster australis, .sp. n. 

 External Characters. 



Length. — The length varies from 0.88 mms. to 1.83 mms. Average 

 individuals measure about 1.4 mms. The largest measured (1.83 

 mms.) was almost divided. 



The prostomium is circular and sucker-like; this is most clearly 

 seen in the living animal, which moves along with a looping move- 

 ment, very much like a leech. The mouth is on the ventral surface; 

 the anus is terminal. At the posterior end there is no definite 

 sucker, Ijut the animal seems capable of slightly flattening its body 

 so as to somewhat resemble one. 



The setae are arranged in bundles; typically there is a pair of 

 bundles of setae in each segment; but after the first pair there is 

 an interval without any setae; the second pair of bundles is in the 

 sixth segment. Then they aie arranged regularly, a pair in each 

 segment, to the posterior end. 



