. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 108 INVERTEBRATE MORPIIOLOOT. i ! m 'â \ are to bo considenui as representing the ancestral form from which both they and the Kotifera liave descended more nearly than the latter group, or wliether they are moditieations of the Kotifer type of structure and havo had tor their ancestors forms whicii were Kotifer-like in structure, it is difficult to say; thougli the balance of evidence seems to tij) in favor of the former view. Attention should be called, however, to a
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 108 INVERTEBRATE MORPIIOLOOT. i ! m 'â \ are to bo considenui as representing the ancestral form from which both they and the Kotifera liave descended more nearly than the latter group, or wliether they are moditieations of the Kotifer type of structure and havo had tor their ancestors forms whicii were Kotifer-like in structure, it is difficult to say; thougli the balance of evidence seems to tij) in favor of the former view. Attention should be called, however, to a possible affiliation of the Oas- trotrutlia with the Echinodera. If, as has been suggested (p. 186), the seg- mentation of the latter has no phylogenetic signiticance, it is not difficult to trace similarities of structure in the two groui)s, the principal differ- ences being connected vvitli external parts. It is by no means improbable tliat the Gastrotriclia, Kotifera, and Echinodera form a series, eacli of the groups being of equivalent rank, and related to each other somewhat as are the Turbellaria, Trenuitoda, and Cestoda. Genus Dinophilus. The geuus Dinophilus includes some small marine organ- isms all of which are ⢠ferable to a small number of species. The body (Fig. 96) is cylindrical and consists of a head segment followed by from 5-7 trunk segments (tlie number varying according to the species), each of which bears a ring of cilia, inter- rupted ventrally by a uniform ciliation which covers the entire ventral surface. The head is likewise provided with a ring of cilia which is usually double, one of the constituent bands passing in front of the mouth and the other behind it, the area in- tervening between these two bands being, in one species at least, occupied by smaller cilia. The musculature of the body-wall is but weakly developed, though both uu external layer of circular fibres and an in- ternal one of longitudinal fibres may be found, both layers bein
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