. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. [120] OVUM. or is rather a collection or aggregation of a number of germs surrounded by a common yolk; in fact, as has been suggested, an ova- rian sac containing a number of ova.* The manner in which the spermatozoa reach the ova for fecundation does not appear to have been ascertained with accuracy. Entozoa.—The ovology of the Helmintha or Entozoa has received considerable atten- tion from physiologists, both on account of the interesting nature of the phenomena pre- sented by its study, and because of the anxiety to d
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. [120] OVUM. or is rather a collection or aggregation of a number of germs surrounded by a common yolk; in fact, as has been suggested, an ova- rian sac containing a number of ova.* The manner in which the spermatozoa reach the ova for fecundation does not appear to have been ascertained with accuracy. Entozoa.—The ovology of the Helmintha or Entozoa has received considerable atten- tion from physiologists, both on account of the interesting nature of the phenomena pre- sented by its study, and because of the anxiety to discover the mode of production of these parasites within the bodies of other animals. From the researches on this subject which have been prosecuted with great assiduity by a number of observers in recent times, not only have many doubtful points been solved as to the origin of the Entozoa, and the views of naturalists greatly modified in regard to the history of these animals, but considerable assistance has also been received in the elu- cidation of general questions in ovology. I will give a short sketch of what has been most recently ascertained on this subject under the three divisions of the Nematoidea, including all the Round Worms, the Trematoda, and the Cestoidea including the Cystica. All the animals belonging to the first division are bisexual, and the production of the embryo is direct from the ovum, without metagenesis or metamorphosis ; in the two other divisions hermaphroditism prevails, and development is indirect, or accompanied by metagenesis and metamorphosis in the greater number. Nematoidea.—The genital organs in the first of these orders present the same favourable circumstances as those of Insects for the ob- servation of the structure and formation of the reproductive elements in their successive stages, as in the different parts of these tubu- lar organs there are to be found at once the spermatic cells and spermatozoa, and the ger- minal cells and
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