. A text-book of invertebrate morphology. Invertebrates. 402 INVERTEBBATE MOEPHOLOGT. that, on the assumption of a sessile life hermaphroditism became character- istic of the order, the bisexualism of these boring forms being secondarily acquired. The fact that the pigmy males present larval characters sug- gests the idea that their occurrence may be an extreme case of proterandry. If in the hermaphrodite forms it is a rule that the spermatozoa mature earlier than the ova, thus preventing self-fertilization, it is conceivable that this early maturation of the testes might be carried back almos
. A text-book of invertebrate morphology. Invertebrates. 402 INVERTEBBATE MOEPHOLOGT. that, on the assumption of a sessile life hermaphroditism became character- istic of the order, the bisexualism of these boring forms being secondarily acquired. The fact that the pigmy males present larval characters sug- gests the idea that their occurrence may be an extreme case of proterandry. If in the hermaphrodite forms it is a rule that the spermatozoa mature earlier than the ova, thus preventing self-fertilization, it is conceivable that this early maturation of the testes might be carried back almost to the Cypris stage and pigmy males be thus developed. Not unfrequently barnacles choose the bodies of other animals upon which to fasten, as for instance upon the cara- pace of Zimvlus, or on the skin of whales, and the genus Andasma fastens itself upon the surface of the body of a Shark, its stalk penetrating into the tissues and developing rootlike processes and so enabling it to lead a parasitic life. As a result of this the calcareous plates cease to develop, the mantle having merely a leathery consistency and the mandibles and maxillae remain rudimentary. This degenera- tion is carried still further in Proteolepas (Fig. 182), which lives as a parasite in the mantle-cavity of other Cir- rhipeds and has a maggotlike appearance, the body being distinctly divided into eleven segments and lacking all traces of a mantle. The mouth-parts are modified so as to be suctorial, and the thoracic feet are entirely wanting, while the digestive tract becomes rudimentary. Finally, a group of forms, known as the Hhizocephala, fasten themselves to the abdomen of crabs and become transformed into cj'lindrical or saclike structures entirely destitute of digestive tract and appendages, rootlike processes arising from the anterior end of the body and traversing the body of the host, by whose juices the parasite is nourished. The genus Sacculina consists of an an- terior short cylindrical port
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
