. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. lay their eggs singly (Fig. 194) while others lay them all at one time in little boat-shaped rafts called egg-boats, the individual eggs standing upright (Fig. 195). The fact that the eggs are a little larger at the lower end makes the whole egg-boat slightly concave, thus making it difficult to overturn. Most of the com- mon mosquitoes of temperate climates lay their eggs on the open surface of water or at- tach them to some partially submerged object; a few species lay eggs which sink. Many species, h
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. lay their eggs singly (Fig. 194) while others lay them all at one time in little boat-shaped rafts called egg-boats, the individual eggs standing upright (Fig. 195). The fact that the eggs are a little larger at the lower end makes the whole egg-boat slightly concave, thus making it difficult to overturn. Most of the com- mon mosquitoes of temperate climates lay their eggs on the open surface of water or at- tach them to some partially submerged object; a few species lay eggs which sink. Many species, however, especially those of the far north and of the tropics, lay their eggs in dry places which are likely subsequently to be covered with water. In T^ ,,^^ T^ c A 17 J • most mosquitoes of temper- liG. 194. t/ggsof Anopheles quadnmacu- . ^ latus on surface of water. X 13. (After ate climatCS the CggS hatch Howard.) • jj ^ £g^ days, or even within 24 hours. In the species of the far north the eggs probably never hatch until the following spring, being laid in depressions on the ground which are usually riot immersed until the melting of the winter snows. Such hibernating eggs are said not to hatch unless they have been exposed to freezing temperatures. On the other hand the mosquitoes of dry hot countries lay eggs which are highly re- sistent to desiccation and do not lose their vitality during months of dryness. Such species must almost "live while the rain falls," and to win in the struggle against an unfavorable cUmate they must be prepared to utilize the most transitory pools for the completion of their aquatic immature stages. In such cases the embryo within the egg shell develops to the hatching point, so that it is ready to begin the larval existence almost with the first drop of rain. Such mosquitoes further fortify their race against the unkind environment by laying their eggs in a number of small batches instead of in a single mass, as is the habit wit
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