OBSERVATIONS CONCERNING FISH-PARASITES. Ill 



Among the subjects which should engage the attention of the helminthologist 

 who takes up the study of fish-parasites I should place first what I will call pioneer 

 work; not because I think it to be of most absolute importance, but because it should 

 precede other kinds of investigation. It is of supreme importance, it seems to me, to 

 have full descriptions, accompanied with sketches, of the adult forms of entozoa which 

 infest the fish of our waters. As much work as possible should, at the same time, be 

 done on larval forms. Whenever larval forms can be certainly identified as the 

 immature form of some adult, or where, as in the case of larval tetrarhynchs, there are 

 constant adult characters present in the larva, there should be full descriptions given, 

 always accompanied with sketches. Date of capture and name of host should, of course, 

 be given in all cases. Incidentally these descriptions should include just as. much 

 anatomical and histological detail as the material at the disposal of the investigator 

 and his time will permit. For most of the entozoa, which are often very variable in 

 shape, the more detailed the description is the better. Furthermore, investigations 

 should be carried on iu every month of the year in which the fish under examination 

 can be obtained. Notes should be made, at the time of collecting, of the food of the 

 fish; this may lead to the discovery of the intermediate host. 



Next, the life-histories of those forms which are already known, or thus become 

 known in carrying on the pioneer work, should be made out. Enough is already 

 known on this subject to furnish, in most cases, a working clue. In this, as in the 

 pioneer work, attention should be given to anatomical and histological details, to 

 which may be added, as occasion offers, embryological details. I think this order 

 is preferable, for the reason that where the investigator is engrossed with the 

 study of the early stages of little known forms, there is danger of confusion resulting 

 from the mixing of descriptions of young forms which are specifically different. This 

 source of error is probably not so likely to arise in the case of the cestodes and nem- 

 atodes as of the trematodes. 



In this connection I may mention two or three cases which occur to me as worthy 

 of further investigation. In almost every specimen of squeteague (Cynoscion regalis) 

 which I have examined, I have found the cystic duct infested with young tetrabothria. 

 They are usually attached in clusters to the wall of the duct, and apparently get their 

 nutriment mainly by absorption from the Avails of the cystic duct, through the scolex, 

 which is provided with a special sucker. When disturbed they easily become detached 

 and fioat about iu the amber-yellow contents of the duct. Forms closely resembling 

 these, though usually smaller, are also frequently met with in the intestine of the 

 same fish. 1 have also found them in the intestine of the goose-fish (Lophius pisca- 

 torius) and in the cystic duct of a flounder. Some of them appear to be the young of 

 an echeneibothrium. If collections were made at other times of the year than the 

 summer, which is the only time I have had an opportunity to collect them, it should 

 not be a difficult matter to identify them and to make out some or all of their life-history. 



Another case of parasitism, or rather condition of parasitism, which calls for 

 special investigation, is that furnished by many of the encapsuled nematodes. In the 

 majority of fish which I have examined, I have found a greater or less number of 

 nematodes, coiled up and enveloped in a thin cyst, and usually attached to or en veloped 

 in the serous investment of the viscera. In many species they are few, but in some, 

 of which Lophius is a notable example, they are very abundant and almost invariably 

 present iu every specimen. These encapsuled nematodes are always immature. I 



