378 William Morton fVheeler 



rod (Solidago canadensis) within an area oi less than a square mile 

 and noted the sex of each individual and the number, sex and posi- 

 tion of the Xenos parasites which had protruded their heads 

 between the gastric sclerites of the wasps, A further study of 

 the form and coloration of the hosts was undertaken in the hope 

 of detecting modifications, like those seen by Perez in stylo- 

 pized Andrenae. My observations, however, gave much less in- 

 teresting results than those obtained by the French naturalist, 

 and I therefore refrained from publishing them and awaited 

 an opportunity to continue them on additional material. This 

 opportunity, however, has not presented itself, so that I have de- 

 cided to give my observations for what they are worth, in the hope 

 that they may be amplified by some other more fortunate ob- 

 server. My preserved Xenos material was turned over partly to 

 Miss Enteman, who published a short paper on the genital ducts 

 of the females ('99), and partly to Mr. C.T. Brues who published 

 a brief account of the embryology of the parasite ('03). The 

 table on the page opposite contains the results of counting the 

 sexes of both host and parasite on the difi^erent dates of collecting. 



From this table the following conclusions, valid only, of course, 

 for the particular summer and locality in which the insects were 

 collected, may be drawn: 



I. Of the total number (1000) of Polistes metricus, 251 or fully 

 25 per cent were stylopized. This is a high percentage, though 

 as will be shown, it has been exceeded in the statistics of other 

 observers. It may be regarded as too great, first because the 

 parasitized individuals, being more sluggish, would be more 

 easily caught, and second, because my interest in such specimens 

 would lead me to exercise greater care in capturing them. I 

 would say, however, in answer to such objections, that I attempted 

 to collect the wasps at random without noticing whether they 

 bore parasites or not, that a long handled net was used in captur- 

 ing them, and that the table con tains onlyspecimens inwbichXenos 

 had already protruded their heads between the gastric segments 

 of the wasps. A number of apparently unifested wasps were 

 dissected and were found to contain larval parasites, so that the 

 actual percentage of parasitism was even greater than that indi- 

 cated in the table. 



