126 



ZOOLOGY. 

 FIG. 62. 



FIG. 62. Lake Lamprey (fetromyzon marinus unicolor) clinging to Sucker. (From 

 Bull. U. S. Fish Commission, by Surface.) 



Questions on the figure. Does it seem that this is an instance of 

 parasitism or simple preying? What special organs has the lamprey adapt- 

 ing it to this habit? What references can you find to the breeding habits 

 of the lamprey? 



success with which this needful function is accomplished shows 

 us that the parasite must be considered well adapted to its 

 conditions, notwithstanding its degeneracy. Its chief hazards 

 are met in the passage from host to host and these are over- 

 come by the carnivorous and omnivorous habits of hosts and 

 the extraordinary powers of multiplication on the part of the 

 parasites. 



161*. Practical Exercises. Enumerate all the parasites, transient and 

 permanent, known to infest man, and find to what groups of animals they 

 belong. Report on the habits of the principal parasites on man : as tape- 

 worm, trichina, etc. What other hosts are demanded to complete the life 

 cycle? What are the principal sanitary conclusions to be reached? Ex- 

 amine the mouth-parts of the mosquito (see Fig. 63). To what kind of 

 feeding are they adapted? 



162. Habits and Instincts in Relation to Adaptation. 



In the study of adaptations there is constant danger lest we 

 come to consider that structures alone are adaptive. In reality, 

 adaptation in the manner of doing things is quite as important 

 as in the structure of the organs by which work is done. 

 When even the simplest organisms are acted on by an external 



