. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 28 POLYPIFERA. the office of ovaries. The ova are, in fact, developed in the substance of the longitudinal membranous folds from which the gemma? sprout. As they grow larger they project internally, and soon become pedunculated ; at last, when mature, they detach themselves from the ovigerous fold and fall into the abdominal cavitv, whence an issue is afforded to them through the mouth of the polype. No ovule is ever developed from the parietes of the abdominal cavity intervening between the longitudinal folds ; and henc
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 28 POLYPIFERA. the office of ovaries. The ova are, in fact, developed in the substance of the longitudinal membranous folds from which the gemma? sprout. As they grow larger they project internally, and soon become pedunculated ; at last, when mature, they detach themselves from the ovigerous fold and fall into the abdominal cavitv, whence an issue is afforded to them through the mouth of the polype. No ovule is ever developed from the parietes of the abdominal cavity intervening between the longitudinal folds ; and hence there can be but little doubt that these lamellae represent the ovaria of the animal. On seeing the same organ producing some- times buds, or gemma;, and sometimes ova, Milne Edwards was led to inquire into the cause of this difference in the mode of repro- duction, which he conceives to be of a me- chanical nature. In those parts of the polype which are not yet imprisoned in the growing mass of the polypary, reproduction is gene- rally effected by the development of external buds, while towards the base of the polypary, where the constituent zoophytes are inti- mately united together by their outer surface and are surrounded by a sort of sheath, no external buds are formed, but the ovules make their escape into the internal cavity of their parent. Hence the distinguished zoolo- gist, whose memoir we quote, is led to infer that, on the one hand, the mechanical ob- stacles to be encountered, and on the other the excitement occasioned by the contact of the surrounding element, determine this dif- ference of procedure, and that the membrane which performs the functions of an ovary produces indifferently either ova or gemmae, according as it finds less resistance or is more stimulated on the inside or the outside of the abdominal walls. From the above details it becomes easy to explain how a single polype, by its repro- ductive powers, can form the complicated mass of the compou
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