. A manual of zoology. Zoology. C(ELUELMi:STUES. 295 In structure tho Rotifiers are much like the trochophore type of embryo of annelids and molluscs to be described later. They must hence be regarded as extremely primitive forms, connected at once with the ancestors of these groups, and, as shown by nervous system and excre- tory organs, with the flatworms as well. Most species are cosmopolitan and inhabitants of fresh water. Many species in America. Near the Rotifera may be placed tlie fresh-water GASTROTRICHA {Ichthydium, Chatonotus) and tlie marine ECHINODERIDvE, forms which are little und
. A manual of zoology. Zoology. C(ELUELMi:STUES. 295 In structure tho Rotifiers are much like the trochophore type of embryo of annelids and molluscs to be described later. They must hence be regarded as extremely primitive forms, connected at once with the ancestors of these groups, and, as shown by nervous system and excre- tory organs, with the flatworms as well. Most species are cosmopolitan and inhabitants of fresh water. Many species in America. Near the Rotifera may be placed tlie fresh-water GASTROTRICHA {Ichthydium, Chatonotus) and tlie marine ECHINODERIDvE, forms which are little understood. PHYLUM YI. CCELHELMINTHES. Tho Co'llielmintlios are distingnished from all the forms which have gone before by the presence of a body cavity, separatmg the outer body wall from the intestine. This cavity is the coelom, but wlietlier it be homologous in different groups, nematodes and annelids, is not settled. The body muscles are developed from tlie. Fig. —Sfu;tion of Ascarix lvrnhrHimU:s through the pharyngeal bulb; bealde it a bit of the body wall more enlarged, c, cuticle: f/, dorsal line ; h, hypodermis; j/j, longitudinal muscle; n, nucleus of muscle cell; jj, muscle cell; .s, lateral line; V, A'entral line ; v\ excretory canal. outer (parietal) epithelial wall of the cadom and hence are ' epi- thelial muscle cells' (figs. 250, 200). The excretory organs con- nect the body cavity with the outer world and hen(;e are nephridia (earlier called segmental organs, cf. fig. 01)). Internally they begin with a ciliated funnel, the nephrostome. and continue as long coiled tul.)es expanding just before the enter end to a kind of bladder. The sexual apparatus is simple. The gonads (fig. 200, o) are. 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 Hertwig, Richard, 1850-1937; Kingsley, J. S. (Jo
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