Monopisthodiscinea 159 



and may accumulate in large numbers in the gill and nasal cavities. In 

 5-8 days ciliated larvae about 225 microns in length are hatched. These 

 swim rapidly, and some eventually become attached to susceptible fishes. 

 Development into the adult is direct. 



Collection and culture. Apparently the organisms may be cultured 

 in any balanced or well aerated closed-system aquarium which contains 

 susceptible fishes, and the problem present in the public aquariums 

 mentioned above is how not to culture rather than how to culture them. 

 However, after infection an immunity is developed by certain species 

 which makes the continual introduction of new hosts advantageous. This 

 is discussed by Nigrelli and Breder (1934). In mild infections the 

 cornea is attacked and sometimes destroyed. Loss of eyes due to 

 secondary bacterial invaders may follow. In heavy infections the epi- 

 dermis may be considerably injured, and the scales may be removed from 

 large areas of the body. Over 2,000 worms have been found on the body 

 of a single fish. Severe infections usually result in death of the host. 

 At the New York Aquarium treatment of infected fishes consists of 

 dipping in "sol-argentum" or similar substances or of raising the density 

 of the seawater by addition of salt (Nigrelli, 1932). 



In the work of Jahn and Kuhn the adults and the attached larval stages 

 were obtained by scraping mucus from the eyes and body surface of in- 

 fected fishes with a sharp scalpel. The mucus was transferred to stender 

 dishes. In about 10 minutes the worms became attached to the bottom 

 of the dishes, and the mucus was pipetted off and the seawater renewed. 

 The process of egg laying, and the movements of the digestive system, 

 etc., were observed with a dissecting microscope within a few hours 

 after collection. The eggs were removed immediately after laying and 

 kept in fresh seawater which was changed several times a day until hatch- 

 ing occurred. The free-swimming larvae were isolated with a pipette. 

 In aquarium systems which contain a filter, the eggs and larvae may be 

 found in the filter chambers in considerable numbers. 



This species offers a very good source of live demonstration material 

 for the life history of monogenetic trematodes, and the above methods 

 seem advisable for the investigation of any monogenetic life history which 

 is similar to that of Epibdella. The application of these methods to other 

 species should be of special interest, for there are no other life his- 

 tories known for the order Monopisthodiscinea. The scarcity of 

 observations on the life histories of members of this group is probably due 

 to the scarcity of well kept closed-system salt water aquaria containing 

 susceptible fishes. Under natural conditions, of course, the free- 

 swimming larvae could be collected only rarely in plankton nets, and 

 this material ordinarily would not be sufficient for the study of life 

 histories. 



