ORIGIN OF CILIATED INFUSORIA 259 



Ciliates have been found to belong to two species, P. phalcenoides 

 and P. sexpundata, as well as another of the same genus but rather 

 larger, and with a narrower abdomen marked by more obvious 

 bands than in either of the other two. They have been met with 

 most frequently in P. phalcenoides, and always only in the females of 

 each variety. That no Ciliate has ever been seen within the 

 abdomen of a male fly, of either of these species, will be found 

 to be a point of great significance. 



Examination of the flies soon showed that they possessed no 

 recognisable alimentary canal. Like their allies, the Harlequin 

 Fly and the Ephemeridse, these Psychodae do not feed, and their 

 brief life in the imago state seems solely devoted to the processes 

 of reproduction.^ When the mature eggs in some, or the Ciliates 

 in others, have been voided, little is to be seen within the abdomen, 

 apart from the vascular system and the air tubes, save a varying 

 number of fatty processes attached to the abdominal wall, and the 

 terminal portions of two brown Malphigian tubules. 



At first I was extremely puzzled to account for the presence of 

 these swarms of Ciliates in some of the flies — especially seeing that 

 they were flies which did not feed and possessed only the abortive 

 rudiments of an alimentary canal. The fact that the Ciliates were 

 found only in female flies (which were also very much more com- 

 mon than the males) was an important point, and soon became all 

 the more important when, on several occasions, I discovered a 

 number of loose immature eggs of various sizes, scattered about 

 among the Ciliates, in different parts of the abdomen. 



What the meaning of these immature eggs being loose in the 

 odominal cavity may be, and how this condition of things is 

 brought about, I am unable to say ; but a careful examination of 

 such eggs, and of the various states of the embryo Ciliates to 

 which I am now about to refer, has forced me to come to the 

 conclusion that the latter have been derived from the former. 



In Fig. 59, A ( X 250) one of the larger of the specimens of these 

 i amature eggs is to be seen, while in B ( x 375) one of the very 



been away, my supplies have been fitful and not very abundant. Some odour 

 appears to attract the flies to this mixture, possibly in connection with their egg- 

 laying instinct. 



' In their work " On the Harlequin Fly," 1900, p. 106, Miall and Hammond 

 say, " It is evident that Chironomus does not feed in the winged state. The 

 mouth parts, though of elaborate structure, are never used in feeding, and the 

 alimentary canal of the fiy is empty, except for a greenish fluid, which fills the 

 stomach of the pupa and newly emerged fly." 



