. Zoology : for students and general readers . Zoology. HABITS OF HOLOTHXJlilANS. 137 semblance bet-ween the two branches (Echinoderms and worms) is one simply of analogy, and involves no blood-rela- tionship. On the other hand the radiated arrangement of parts and the development and relations of the water-vas- cular system ally them, through the Ctenophores, with the Actinozoa and Hydroida, and it seems more natural to re- gard the Echinoderms as forming a branch of animals in- termediate between the Hydroida and the worms, there being certain low worms with a water-vascular system. But the
. Zoology : for students and general readers . Zoology. HABITS OF HOLOTHXJlilANS. 137 semblance bet-ween the two branches (Echinoderms and worms) is one simply of analogy, and involves no blood-rela- tionship. On the other hand the radiated arrangement of parts and the development and relations of the water-vas- cular system ally them, through the Ctenophores, with the Actinozoa and Hydroida, and it seems more natural to re- gard the Echinoderms as forming a branch of animals in- termediate between the Hydroida and the worms, there being certain low worms with a water-vascular system. But the student will be better able to appreciate these general questions after a more or less thorough acquaintance with the forms and structure of the pres- ent group. For this purpose he should first examine living sea- cucumbers, and then carefully dissect them. A detailed study of the anatomy of a Pentacta or a Holothuria, one a northern the other a subtropical and tropical form, and of a Synapta, found everywhere along our coast in sand below tide-marks, will give the groundwork ; and this knowledge, autoptically acquired, can then be corrected and extended by reading monographs or compiled state- ments to be found in the more authoritative general works on comparative anatomy. Living Holothurians can be pro- ^""^ Tenney-s zoology, cured with the dredge or dug out of the sand between tide- marks. They should be kept in aquaria, and their move- ments watched as well as their mode of locomotion, and the action of their branchiae or external gills (tentacles). The common sea-cucumber, north of Cape Cod, and ex- tending through the Arctic regions around to Great Britain, is Pentacta frondosa Jaeger (Fig. 88). It lives from ex-. —Pentacta 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 Packar
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
