TA EPIZOA. 



21 



the different stages from temporary parasitism to the pure para- 

 site. Take, for example, the flea {Ptdex irritans), the bedbug 

 {Cirncx Ledularia), and the leach {^Hlrudo medicinaUs). These 

 seek their nourishment alone on their hosts for the time being, 

 but can, at least, and generally do, spend the rest of their exist- 

 ence in an independent life, and develop from the egg, and spend 

 their youth and adolescence, independently of their host ; and 

 indeed some of this same class of in^ects may lead an entirely 

 independent existence. And if so, we should look for difierences 

 in the organic make-up gradually growing up between members 

 of the same family, namely, between those that lived an entirely 

 independent existence and those that were most attached to the 

 jmrasitic mode of life. 



I speak now only of those parasites that attach themselves 

 temporarily to the surface of the animal upon which they live. 

 Of course in the case of those that infest the internal economy of 

 an animal the difference would evidently be much greater. 



In those animals in which parasitism is a long continued 

 heredity, many of the original traits and organs of independent 

 existence have almost or entirely disappeared. I am. not well 

 posted in this branch of zoology, but I imagine it would be pretty 

 difficult to make out the original habitat and mode of existence 

 of such old-time sponges as ■pediculus cayitis, P. vestimenti, P. 

 Tdbesantum and PliithirivH ingninalu, for these, as far as I know, 

 have ceased entiiel}' their independent existence, and utilize 

 their host not only for their nourishment but (in contradistinction 

 to the temporary parasite before mentioned) they spend their en- 

 tire existence, lay their eggs, and bear theii young on the sur- 

 face of the body of their adopted hosts. 



Now, what I wanted to speak of more particularly in this 

 article is a family of parasites that are usually classed as tem- 

 porary parasites, I believe — viz., the family of Ixodicv, or Ticks. 



There are many genera under this family, about twelve. I 

 believe — Ixodes hovis^ I. ricinus, J. albijActus, I. Boiit^tnii and four 

 or live others under the classification of /, ylinmcf/Jius, etc. 



I received a number ot specimens of the species Dcrniaccntor 

 Americrtnm L., taken from the body of a male caribou killed in 

 the first week of February, 1898. I put them in a glass bottle, 

 and what struck me particularly was their extreme l(!naoity of 



