. Animal parasites and human disease. Insects as carriers of disease; Medical parasitology. Fig. 194. Eggs of Anopheles quadrimacu- latus on surface of water. X 13. (After Howard.) lay their eggs singlj^ (Fig. 194) while others la}' 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 mosciuitoes of temperate climates lay their eggs on the open surface of water or at- tach
. Animal parasites and human disease. Insects as carriers of disease; Medical parasitology. Fig. 194. Eggs of Anopheles quadrimacu- latus on surface of water. X 13. (After Howard.) lay their eggs singlj^ (Fig. 194) while others la}' 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 mosciuitoes 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. Manj^ species, h o w e v e r, 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 most mosquitoes of temper- ate climates the eggs hatch in a few 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 usuaUy not 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 liot 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 climate they must be prepared to utilize the most transitory pools for the completion of their acjuatic 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 enviromnent l)y laying their eggs in a number of small l)at(' instead of in a single nuvss, as is the habit with. Fig. 195. Eg
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmedical, bookyear1918
