240 



MONOGRAPH OF THE LABOULBENIACE^E. 



Variations in size among different specimens of a given species are often influ- 

 enced by two factors, namely, the size of the host and the position in which the para- 

 site has become attached. Thus small specimens of a given species of insect will, as 

 a rule, bear smaller parasites than larger ones, and the same is true of smaller species 

 in a varied genus, for example, like Platynus, almost all the members of which are 

 liable to be infested by a single species of Laboalbenia. In regard to differences de- 

 pendent on the position of growth, it is usually true that individuals growing near the 

 circulatory centres of the host, being presumably better nourished, are commonly dis- 

 tinctly larger. The largest individuals that I have observed, for example, have been 

 found growing on the thorax or prothorax about the base of the two anterior pairs of 

 legs, while, on the same insect, those which inhabit the tips of the elytra, or of the legs, 

 include the smallest specimens. It should also be observed that individuals growing 

 in situations in which they are exposed to the most unfavorable conditions are apt to 

 be thick-set, short, and stout, with short appendages. This is true, for example, in 

 specimens of Laboulbenia elongata, L. subterranea, and various other' species, when they 

 occur, as they not infrequently do, on the mouth parts or near the tips of the legs of 

 their hosts, the difference in general habit in such cases being often so great that such 

 forms might easily be mistaken for distinct species. The same short, stout habit, it 

 may be mentioned, characterizes species which are found normally in such situations 

 and not elsewhere ; as, for instance, in the case of Laboulbenia parvula, PeyrtischieMa 

 minima, and others, that are, as a rule, found near the extremities of the legs, and only 

 exceptionally in other situations. 



The rate of growth of the Laboulbeniacese and the duration of their life period are 

 matters concerning which it is not easy to make exact observations, owing, on the one 

 hand, to the difficulty of obtaining freshly hatched hosts that have not been exposed 

 to infection, and, on the other, to the uncertainties connected with the determination 

 of the exact time at which the infection of the fresh hosts is accomplished. By keep- 

 ing in confinement insects which have been collected with spores upon them just 

 germinating and distributed on definite areas, one may estimate with considerable 

 accuracy the time necessary for the fungus to reach maturity. This period, in the 

 species of Laboulbenia which I have thus cultivated, has proved to be from two to three 

 weeks. It is doubtless variable, however, in different genera ; those which are more 

 complicated in structure requiring, for their full development, a period correspondingly 

 longer ; as may well be the case, for instance, in Rhachomyces or Zodiomyces. 

 According to Peyritsch, freshly hatched flies confined with others infested by Stigma- 

 toiwjces Baeri were found to bear mature individuals of the fungus in from ten to four- 



