. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 240 INVERTEBRATE MORPHOLOG T. undoubtedly homologous with the nephridia of the Chffitop. oda, possessing the same relations. In a few forms {BonelUa, Phascolion) a single nephridium only is present. In addition to these in Echiurus, Thalassema, and allied genera there is a usually much-branched organ on either side lying in the body- cavity and opening into the terminal portion of the intestine. Numerous ciliated funnels occur upon the branches placing the organ in comm
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 240 INVERTEBRATE MORPHOLOG T. undoubtedly homologous with the nephridia of the Chffitop. oda, possessing the same relations. In a few forms {BonelUa, Phascolion) a single nephridium only is present. In addition to these in Echiurus, Thalassema, and allied genera there is a usually much-branched organ on either side lying in the body- cavity and opening into the terminal portion of the intestine. Numerous ciliated funnels occur upon the branches placing the organ in communication with the body-cavity. This so- called " respiratory tree " (so named from a supposed homol- ogy with the similarly named organs of the Holothuria (q. v.) are probably nephridia, though whether or not they per- form excretory functions is not quite clear. In Priapulus these organs are represented by branched tubes, the branches of which terminate blindly in flame-cells, resembling thus the excretory organs of the Platyhelminths, and in Sipunculus rudiments of these organs have been described as short tubes. The Gephyrea are bisexual, the reproductive organs {oc) forming small digitate, elongate, or ovoid processes arising from the peritoneal lining of the body-cavity; but in some forms {Sipunculus) their products early escape into the ca> lomic cavity, in which they float. The exact manner in which the ova and spermatozoa escape to the exterior has not been definitely ascertained for the majority of forms, but it seems probable that the nephridia serve as the generative ducts. In Priapulus the " respiratory trees " are said to give rise to the reproductive organs, and also to serve as the reproductive ducts—a behavior which would render exceedingly probable the supposition that they are modified uepliridia. Two orders are recognizable in the 1. Order EchiuresB. The Echiureae, sometimes known as the Gephyrea armatu, are characterize
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