. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. it::Ti:iiOGAMi. 127 discovered process known as heterotjamy. It is characterised bv the succession of differently organized sexual generations living under -diflerent nutritive conditions. Heterogamy, which was first discovered in certain small Nematodes (R/iahdonema niyrovenosum and Leptodera cqypendiculata), can scarcely be explained otherwise than as an adaptation to changed conditions. For when the embiyo is developed as a puiitsite in conditions favour- able for the acquisition of nutriment, it
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. it::Ti:iiOGAMi. 127 discovered process known as heterotjamy. It is characterised bv the succession of differently organized sexual generations living under -diflerent nutritive conditions. Heterogamy, which was first discovered in certain small Nematodes (R/iahdonema niyrovenosum and Leptodera cqypendiculata), can scarcely be explained otherwise than as an adaptation to changed conditions. For when the embiyo is developed as a puiitsite in conditions favour- able for the acquisition of nutriment, it gives rise to a sexual form so diffeient in size and structure frjm that which arises if the. Fig. Hi.—a, Rhabdonema ninrrovenosum of aLout 3o mm. in length at the stage when the male organs are ripe. G, genital trland; O, mouth ; D, alimentary canal; ^, anus ; A, nerve ring; Dr.:, gland cells; Z, isolated spermatozoa. B, Male and female Rbabditis, length from about 1 o to 2 mm. ; Oo, ovary ; T, testis; V, female genital opening; Sj^, spicula. embryo leads a free existence in damp earth or dirty water {, in conditions not so favourable for the acquisition of nutriment), that we .should, from the difference in their structure, place the two forms in different genera. Ehabdonema nigrovenosum from the lungs of Batrachians and the free-living Rhabditis follow each other in a strictly alternating manner (tig. 114, A, B), Other cases of hetero- gnrny are afforded by the Bark-lice (Chermes), and the Eoot-lice. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Claus, Carl, 1835-1899; Metcalf Collection (North Carolina State University). NCRS. London, Swan Sonnenschein
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
