PARASITES FREE WHILE YOUNG. 159 



phases of its evolution. It was at first thought that we 

 had before us an echinoderm in the act of transforma- 

 tion. I wrote to J. Miiller immediately after the dis- 

 covery which he hastened to announce to me, to state 

 that in my opinion, this was only a new instance of para- 

 siticism ; parasites are, however, so rare in this class of 

 animals, and their mode of life is so exceptional, that 

 one ought not to be surprised that this fact did not 

 receive at first its true interpretation. 



Professor Semper found at the Philippine Islands, in 

 the Holothuria edulis, another species of Entoconcha 

 which appears to attach itself to the anal veat of this 

 echinoderm. He gave it the name of Entoconcha 

 Mulleri. We have in it a new example of the relations 

 which certain parasites bear to their hosts, and which 

 are the same in both hemispheres. 



The Lichnophorte are infusoria, allied to the Vorti- 

 cellm, whose form they assume; these are "mimic 

 specites," or mocking forms, of the Trichodinae. One 

 species, the Lichnophora Auerbachii lives on the 

 Planaria tuberculata ; the other, the L. Cohnii, on the 

 branchial membranes of the Psyrmobranchus protensus. 



The associations in the inferior ranks of animals have 

 functipns which are of the highest importance ; some to 

 maintain harmony and health in all that possess life, 

 others to sow the seeds of death, throughout whole 

 regions. There are, in fact, associations in the ranks of 

 the infinitely small creatures, which sometimes have the 

 effect of purifying and rendering more healthful, some- 

 times of destroying. It is among these beings, invisible 

 to the naked eye, that we must seek for the cause of 

 some epidemic diseases. We have here an example of 



