130 NOTES ON GYRODACTYLUS 



only a short time. A repetition of the experiment afforded 

 closely similar results. Distilled water killed many of the 

 animals in six minutes and all were dead in twenty three minu- 

 tes. Here also repetitions gave little deviation from these 

 results. The control animals in normal sea-water were held 

 for twenty-four hours and showed no effects of their detach- 

 ment from the host other than an increase in motor activity 

 undoubtedly due to hunger. The introduction of a little 

 Fundulus blood into the watch-glasses after this period of star- 

 vation invariably caused them to become tiemendously active 

 in the most agitated and entertaining manner, as they would 

 fling themselves end over end along the surfaces of the glass 

 as if in deliberate search of a new host. 



For the purpose of ascertaining the exact cause of death, 

 whether due to the loss of blood or to introduced secondary 

 infections of other organisms, a close examination was made 

 of hosts which had succumbed to the effects of the parasites. 

 The histological picture clearly showed that other organisms 

 were not involved but that death was undoubtedly due to the 

 direct loss of blood caused by the collective feeding activities 

 of the great numbers of these minute trematodes, each of which, 

 individually, could alone cause but trifling damage. The fins, 

 lips and borders of the eye orbits were the regions on which the 

 parasites were most numerous but when infection became heavy 

 the Gyrodactyhis occured over the whole external surface of the 

 host including the scales and even the cornea of the eye. Their 

 activity is most remarkable. The animals constantly shift 

 from place to place and attach themselves by means of their 

 two retractile cephalic lobes and their caudal disk which is 

 powerfully armed with hooks. The host suffers the loss not 

 merely of the blood upon which they feed but also the diffuse 

 haemorrhages which drain from the innumerable, minute per- 

 forations that the parasites inflict. This is the direct cause 

 of death. 



