Two entirely distinct groups, Monadina and Hetero mastigia.
A"', Second longitudinal (in Hetero- nemertini).
Heterocyclic rings may be systematically surveyed from two aspects: (I) by arranging the rings with similar hetero-atoms according to the increasing number of carbon atoms, the so-called " homologous series "; or (2) by first dividing the ring systems according to the number of members constituting the ring, and then classifying these groups according to the nature of the hetero-atoms, the so-called " isologous series."
One or two benzene nuclei may suffer condensation with the furfurane, thiophene and pyrrol rings, the common carbon atoms being vicinal to the hetero-atom.
Typical formulae are (R denoting 0, S or NH): Isomers are possible, for the condensation may be effected on the two carbon atoms symmetrically placed to the hetero-atom; these isomers, however, are more of the nature of internal anhydrides.
Proceeding to the six-membered hetero-atomic rings, the benzo-, dibenzoand naphtho-derivatives are frequently of great commercial and scientific importance.
Albumoses and peptones are white powders, readily soluble in water, with the exception of the hetero-albumoses - a subdivision of primary albumoses.
Chemically; while, in most living things, mere hetero geneity is exchanged for a definite structure, whereby the body is distinguished into visibly different parts, which possess different powers or functions.
In the first of these books his nomenclature is unfortunate; his division of ethical theories into the " unpsychological," " idiopsychological," and the " hetero-psychological," is incapable of historical justification; his exposition of single ethical systems is, though always interesting and suggestive, often arbitrary and inadequate, being governed by dialectical exigencies rather than historical order and perspective.
Both Hetero- and Metane- mertini have been more exhaustively studied than the other two groups, the first, as was noticed above, being characterized by peculiar larval forms, the second developing without metamorphosis.