CHAPTER XXIV 



LAB OULBENI ALES 



The Laboulbeniales form their fructifications only on the chitinous 

 integument of living insects. When examined in situ they appear like 

 minute, dark-colored or yellowish bristles or bushy hairs, usually scattered, 

 but often densely crowded over certain areas on which they form a furry 

 coating. Although they may be said to produce a contagious cutaneous 

 disease, they give rise to no fatal epidemics, such as are sometimes associ- 

 ated with Cordyceps and Entomophthora. The very existence of these 

 parasites seems to depend on the fact that the host is not destroyed, since 

 their own life ends with that of the insect. The habit of growth is exter- 

 nal, unassociated with extensive development of haustoria, except on 

 certain groups of soft-bodied insects, where widely divergent groups have 

 developed extensive rhizoidal processes of the basal cell, which penetrate 

 the interior of the host. 



Such an external parasitism on living and usually actively locomotive, 

 often aquatic hosts, is associated with a comparatively simple structure 

 adapted to the exigencies of such a life. A simple receptacle is fixed by 

 means of a usually blackened base or foot, to the integument of the host. 

 This receptacle gives rise to certain appendages, commonly connected 

 with the production of the male sexual organs, while perithecia are usually 

 produced from the same receptacle, except in certain dioecious groups. 



Most species of Laboulbeniales are limited to definite genera of 

 insects and in a few instances, e.g., Chitonomyces on Gyrinidae and Lacco- 

 phili, even to definite restricted areas of attachment in different host 

 individuals of different species, from even different regions. For example, 

 not only will the distance from the apex of the elytron of the area occupied 

 by a given species always be about the same, but its relation to either 

 margin will be more or less definitely fixed. Of species inhabiting the left 

 elytron, none will be found even in a corresponding position on the right. 



The Laboulbeniales may be divided into three families, distinguished 

 by the relative development of the male sexual apparatus. In the more 

 primitive Ceratomycetaceae, the antheridia are exogenous, bearing free 

 spermatia on the specialized branches of appendages. In the Laboul- 

 beniaceae, the spermatia are produced in unicellular, flask-shaped anther- 

 idia, while in the Peyritschiellaceae the antheridia are compound, 

 discharging the spermatia into a common cavity, from which they are 



subsequently expelled. 



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