The Sunfish as a Host. . 83 



these singular creatures. In their view, the question as to 

 whether the company of entozoa be acceptable or not to the 

 tc host " in no way prevents the invaders being recognized as 

 guests, whilst in most cases they are sumptuously entertained, 

 although they be not welcome. The organization of the 

 entozoa admirably adapts them for a temporary residence 

 within the body of the selected " host •/' so much so, indeed, 

 that from their peculiar organization, one might fairly argue 

 their legitimate title to such an abode ; yet, at the same time, 

 it must be admitted that the means of entry at their command, 

 as well as the instincts they exhibit in their mode of gaming 

 access, do but epitomize the instincts of the genuine burglar. 

 In few cases, if in any, can it be shown that the presence of 

 animal parasites confers positive good to the " host •" but in 

 numerous instances it is certain that they cause incalculable 

 mischief. This was sufficiently shown in our paper on Fasciola 

 hejpatica, in the first volume of the Intellectual Obseevee, and 

 the subject has since been further elucidated by Professor 

 James Beart Simonds, in his instructive memoir on the Nature, 

 Cause, Treatment, and Prevention of the Rot in Sheep. 



If the mere variety of parasites formed an accurate criterion 

 of the hospitality, so to speak, of any given " host," the species 

 here selected for the purpose of illustration might certainly be 

 regarded as a very liberal individual ; but it often happens that 

 an animal liable to harbour only one or two forms of entozoa is 

 more copiously infested by those few particular kinds than 

 another animal which is liable to be infested by a much greater 

 variety of parasitic guests. The short sunfish (Orthagoriscus 

 mola of Schneider, and Tetradon mola of Linnseus) is believed 

 to be infested by nine species of helminths, three of which are 

 usually attached to the gills, while a fourth adheres to the sur- 

 face of the body. All of the latter, though ecto-parasitic in 

 their habits, are true flukes belonging to the genera Distoma 

 and Tristoma, and cannot therefore be removed from the 

 entozoa properly so called. In the present communication we 

 propose to treat only of one of the above-mentioned " guests," 

 selecting for this purpose a species which belongs to the great 

 tapeworm family. We are aware that to some persons the 

 study of this group of animals appears to be peculiarly unin- 

 viting; but in our own experience, based upon a prolonged 

 contemplation of their structure, habits, and development, we 

 can testify to the rare instruction and pleasure which such a 

 research is calculated to afford. 



Notwithstanding the light which experimental investigation 

 has lately thrown upon the subject, the tapeworms are still re- 

 garded by many as individual animals, possessed of long jointed 

 bodies, whereas the organism usually called a tapeworm — like 



