Certain phases of the subject of wandering nematodes have been reviewed recently, particularly with reference to the kinds of nematodes known to be involved, and to the changing views as regards their host-parasite relationships (Beaver, 1956). The clinical aspects also have been summarized (Platou and Beaver, 1956). In the present discussion an attempt will be made to review this subject somewhat more briefly, and to mention some of the questions raised by recent observations. References to original sources included in the reviews just mentioned will be omitted except in a few instances.
Present day species of hosts and parasites have evolved under a gradual flow of diverse ecological situations resulting in more or less fixed host-parasite associations which justify the general concept that certain parasites belong to certain hosts. At the same time, it is recognized that the relationships between hosts and parasites are in most instances somewhat flexible, and that there are degrees of suitability for each other.