648 PROCEEDINGS OF THE NA TIONA L MVSEVM. vol. xxv. 



hosts for any distance inland. Through the kindness of Mr. Vinal N. 

 Edwards man}" specimens of these two species were removed from 

 their hosts, placed in fresh salt water, and sent through the mail from 

 "Woods Hole to Westtield, Massachusetts. 



The A. laticauda were taken from eels and had evidently just fin- 

 ished their egg laying; the A. megalops were from flat fiish (Para- 

 lichtky.s) and were still full of eggs. Some of the females laid upon 

 the sides of the bottle on the way, and the remainder deposited their 

 eggs after reaching the laborator3^ 



But how could any experiments upon a change of host be tried with 

 these forms ? No marine fish were obtainable alive, and if they could 

 have been procured, sufficient salt water to keep them was manifestly 

 out of the question so far inland. 



It was remembered that these parasites infest many fish, like eels, 

 salmon, herring, etc., which are migratory in their habits, and some 

 which pass from salt into fresh water, or the opposite, during their 

 migrations. It becomes an interesting question, therefore, whether 

 the parasite is able to accompany its host through these changes 

 or not. 



It was determined first to try a change from salt to fresh water 

 without the presence of an}- host whatever. Accordingh' several 

 specimens of each of these two salt-water species were placed in a dish 

 of salt water, which was then slowly changed to fresh by the addition 

 of a few drops of the latter at a time. 



The}^ gave apparentl}^ no attention whatever to the change, but 

 continued to swim about in the fresh water as they had done in the 

 salt. Indeed, they manifested so little appreciation of the change 

 that another lot was transferred directh' from salt to fresh water. 

 These appeared a little irritated at first, but quickly recovered and 

 manifested no subsequent difference in demeanor. Then a host 

 was supplied them in the shape of a small minnow, to which the}^ 

 attached themselves readily and upon which the}^ lived for several 

 days. 



These experiments woidd indicate very strongly that Argulus at 

 least, among the copepods which infest the various salt-water migra- 

 tory fishes, is capal)le of contiiuiing upon its host as the latter passes 

 up some fresh-water river in search of a suitable spawning place. It 

 furnishes good proof also that the salt-water as well as the fresh- water 

 forms are capable of changing about from one species of host to 

 another. 



In this connection it is well to recall the fact that the species catos- 

 tomi was first discovered in the Mill River near New Haven, Con- 

 necticut, where the water is distincth^ brackish (1837). 



The same specdes was afterwards found by Gage (1886) in Cayuga 

 Lake, Ithaca, New York, in perfectly fresh water. It has also been 



