Archive image from page 122 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana05todd Year: 1859 OVUM. [109] the nature of this structure in the mature ovum of Anodonta. In this family of Mollusca the micropyle forms a small but very apparent funnel-shaped projection from the surface of the outer mem- brane ; and its hollow nature may easily be ascertained by the fact that the fluid and granular yolk-substance may be forced through it from within. The yolk ball is placed ex- centrically within the vitelline membrane, the inner surface of which it touches
Archive image from page 122 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana05todd Year: 1859 OVUM. [109] the nature of this structure in the mature ovum of Anodonta. In this family of Mollusca the micropyle forms a small but very apparent funnel-shaped projection from the surface of the outer mem- brane ; and its hollow nature may easily be ascertained by the fact that the fluid and granular yolk-substance may be forced through it from within. The yolk ball is placed ex- centrically within the vitelline membrane, the inner surface of which it touches just at the place where the micropyle is situated. From a variety of observations, it has been Fig. 73 . Structure and Formation of Ova in Acephala. (.From Lecaze Duthiers.') a. Portion of the ovary with three pediculated ovicapsules and contained ova from Cardium rusti- curn, magnified 400 diameters; the micropyle is afterwards formed at the place where the pe'dicles are detached from the secreting coaca of the ovary. b. Unripe ovum of Spondylus gtederopus magni- fied 170 diameters, showing the remains of the cap- sule at the upper part, and the projection of the vitelline membrane at the same place where the micropyle is situated. c. Kipe ovum of the same burst by pressure, showing the escape of some yolk granules through the micropyle and into the space between the yolk and the outer membrane. Iii'this and the previous figure the double state of the macula is represented. shown that the micropyle of the Acephalous Mollusca owes its origin to the early pediculated attachment of the ovum. This has been fully brought out by the observations of Hesslin'g in Unio and Anodonta, of Leydig in Venus, and of Lecaze Duthiers in Cardium and some other genera. From these observations it appears that the ova first arise in the ova- rian stroma by the formation of the ger- minal vesicles, as in most other animals, eacli vesicle possessing a distinct single macula. These vesicles come
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