A Student's Text-Book of Zoology Volume 3

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 edition. Excerpt: ...and, in association with this feature, in the presence of free larval stages in the development; in the participation of all segments of the thorax in the formation of the cephalothoracic shield; in the short capsular heart; the absence in the adult of a lacinia mobilis on the mandible (see p. 438) (though there are indications of it in some larval stages) and in the spherical or vesicular shape of the spermatozoa. The Holotropha, on the other hand, agree with the Cumacea, Chelifera, Isopods and Amphipods in the possession of a brood pouch, in which the young are developed until the full number of appendages is attained. The terga of only the most anterior (or none? Lophogastridae), of the thoracic segments are involved in the dorsal shield, the heart is elongated, a lacinia mobilis is present, and the spermatozoa, so far as they have been observed, are filiform. The two groups also appear to be contrasted in the number of segments of the thoracic limbs, the point at which the main flexure of the limb occurs and in the possession by the limb of a terminal claw. In reviewing these differences, to several of which attention has been called by Boas and Hansen, Caiman has proposed the name Peracarida for a group containing all Eumalacostraca possessing a brood pouch, and in this the Holotropha are included, while the Hemitropha are united with the Decapoda in the group of the ' Eucarida." The division, Schizopoda, would, on this arrangement, cease to exist. While admitting that there is much to be said in favour of the course proposed, it appears preferable, in the present work, to retain the group Schizopoda. Zoologists are far from being agreed on the change, and it was strongly resisted by Claus. f Were it adopted the relations of...