. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 60 POPLITEAL REGION. looks upon as being the testis, his opinion being founded on the fact that when a mature specimen of the animal is placed between two plates of glass, and gently compressed so as to rupture its parietes and cause the escape of the viscera, spermatozoa are discoverable in the one and ova in the other. The sper- matozoa exhibit considerable vivacity in their movements, have a disc-like body and a cau- dal filament, and are proportionately of large size ; around them may be seen multitudes of free cellu
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 60 POPLITEAL REGION. looks upon as being the testis, his opinion being founded on the fact that when a mature specimen of the animal is placed between two plates of glass, and gently compressed so as to rupture its parietes and cause the escape of the viscera, spermatozoa are discoverable in the one and ova in the other. The sper- matozoa exhibit considerable vivacity in their movements, have a disc-like body and a cau- dal filament, and are proportionately of large size ; around them may be seen multitudes of free cellules without caudal appendages, which are apparently young spermatozoa. In some individuals the spermatozoa are so numerous that the intestinal canal appears completely enveloped by them, and the whole peri-intestinal cavity seems alive with their movements. In the mature ovary ova are discoverable in different degrees of development, in each of which the vesicles of Wagner and of Purkinje are, according to Professor Van Beneden, dis- tinctly visible. In those ova which approach their complete maturity an external vitelline membrane, or chorion, and a vitellus are per- ceptible, but the two vesicles above men- tioned have disappeared. When arrived at the proper term the ova break from their envelope, or ovisac, and fall into the general cavity of the body, where they move freely about surrounded on all sides by spermatozoa. At length the eggs accumulate in the interior of the body, near the base of the tentacula, and their escape, as witnessed by Van Beneden in Laguncula repens, is at length ac- complished in the following manner. An egg presents itself at an orifice, situated in the vicinity of the anus, through which its external membrane partially protrudes, constituting a sort of hernia (fig. 61, p). The vitellus gra- dually flows from the still enclosed portion of the egg into that which is external, and when the vitellus has thus entirely passed out, the egg is found sepa
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