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."
A"', Second longitudinal (in Hetero- nemertini).
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.
Two entirely distinct groups, Monadina and Hetero mastigia.
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.
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.
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.
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.
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.