SIZE OF MESH 361 



Goeldi refers to this screen question, both in regard to the yellow-fever mos- 

 quito and to the common rainwater-barrel mosquito, in connection with some 

 very interesting observations about the range of variation in the size of the 

 individuals of the same species, a fact which is frequently noticed with other 

 insects but to which special attention has not been called elsewhere with 

 mosquitoes. 



" Frequently I have observed, both in Stegomyia fasciata and in Culex fati- 

 gans, alongside of individuals of normal stature, individuals very much smaller 

 — veritable dwarfs. This observation may be made on specimens captured in 

 freedom as well as on those in captivity, in this last case the phenomenon re- 

 peating itself rather frequently. There are sometimes born individuals, both 

 males and females, so small that they easily pass through the mesh of wire 

 gauze much closer than the mesh of ' Grassi's gauze ' which today is produced 

 on a large scale in Italy with a view to the prophylaxis against Anopheles and 

 malaria (Grassi, himself, recommends a gauze that shall not have less than nine 

 meshes in 1^ centimeters of distance, which corresponds to little linear squares 

 1.7 mm. to the side) . The government of the State of Para imported from Italy, 

 for my experiments, a gauze under this name which had but six threads to 1^ 

 centimeters of linear extension, corresponding to squares of 2^ mm. along one 

 side. I refer particularly to this last brand, which I consider sufficient as a rule, 

 for application to hospitals, to impede the invasion of mosquitoes from outside, 

 but which I found, nevertheless, insufficient for the walls of my cages destined 

 for experiments on mosquitoes like Stegomyia fasciata and Culex fatigans in 

 captivity. 



" In general, the phenomena of macrosomia and microsomia in plants and 

 animals are related directly with greater or less abundant nutrition, and I do 

 not believe that the quoted dwarf race of Stegomyia and Culex is to be explained 

 in any other way than by a sparse alimentation and a delayed development in 

 the larval stage. On this point I have at hand experiments in proof : Larvae 

 bred in clear water — that is to say, relatively poor in assimilable substances — 

 gave me imagos of small stature. Furthermore, it is yet to be shown that I am 

 deceived in my opinion that the frequency of dwarf individuals captured in 

 freedom is not notably greater at certain periods, assuming almost the character 

 of a rule. Thus this year, in the last weeks of October and in November, before 

 we entered fully upon the rainy season, I got the impression that the females 

 of dwarf dimensions were particularly numerous. I doubt that this is the work 

 of a mere accident : it is very possible that the frequency of dwarf individuals, 

 normally possible during the whole year, may be periodic and represent a case, 

 somewhat diminished, of what is called in entomology ' dimorphism of seasons.' 

 Theoretically there can be no serious obstacle in accepting the argument that in 

 the height of the dry season, with the growing lack of water, the conditions of 

 life for the larvae become more difficult, thus favoring the generation of mos- 

 quitoes below the normal dimensions. Impoverished water and reduced food 

 may really, as we have seen above, oblige the larva to take two or three times 

 the period normally necessary for its development and to acquire the necessary 

 growth for its metamorphosis. I have the feeling that hibernation, in the sense 

 in which this word is accepted in zoologic literature, may well for the tropical 

 and equatorial Culicidae find its expression in two ways: (1) Delayed develop- 

 ment of the larvae; (2) Dwarfed stature of the imagos." 



Note hy Translator. — Doctor Groeldi enters into a long explanation as to hiberna- 

 tion, evidently for the benefit of equatorial readers who might accuse him of the mal- 

 use of technical terms. He refers to the phenomenon of " seasonal lethargy " and 

 endeavors to trace a connection between the circumstances favoring the development 

 of the perfect insects in parallelism with the " periodicity of yellow fever." His final 

 paragraph is as follows: 



