A Monograph of the Najades of Pennsylvania Vol. 4 No. 6
A Monograph of the Najades of Pennsylvania Vol. 4 No. 6
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long (smaller than in the instance just mentioned) which is gravid, but has at least three distinct growth-lines, and consequently would be at least in its fourth year.
All other females observed, sterile or gravid, had at least three growth-rests, and should be considered as being in their fourth year of age, or older.
Thus it becomes apparent, that the female structure, at least in some species, develops as early as the second year, and that one at least (Symphynota viridis) may already becom...e sexually mature at this time. In others, the female structure is distinctly seen in the third year, and some of them (Lampsilis nasuta) may bring forth progeny. Later, from the fourth year onward, the time of maturity is reached in most of the species.
F. Differentiating structures of the edge of the mantle.
Simpson in the diagnosis of a number of genera states that the edge of the mantle is "double." According to my observations, it is double along its whole extent in all forms. While the outer edge is closely adjacent to the margin of the hard shell, and is always simple, the inner edge, which is generally parallel and close to the outer edge, is more or less expansile, and is able to fill and close the gap between the two halves of the shell, when the adductor muscles relax, that is to say, when the shell "opens." And further, this inner edge of the mantle is not uniform in its structure all along its margin, but shows certain differentiating structures, some of which are systematically valuable.
What to read after A Monograph of the Najades of Pennsylvania Vol. 4 No. 6?
You can find similar books in the "Read Also" column, or choose other free books by Ortmann, A. E. (Arnold Edward), 1863-1927 to read onlineMoreLess
To quickly assess the difficulty of the text, read a short excerpt:
long (smaller than in the instance just mentioned) which is gravid, but has at least three distinct growth-lines, and consequently would be at least in its fourth year.
All other females observed, sterile or gravid, had at least three growth-rests, and should be considered as being in their fourth year of age, or older.
Thus it becomes apparent, that the female structure, at least in some species, develops as early as the second year, and that one at least (Symphynota viridis) may already becom...e sexually mature at this time. In others, the female structure is distinctly seen in the third year, and some of them (Lampsilis nasuta) may bring forth progeny. Later, from the fourth year onward, the time of maturity is reached in most of the species.
F. Differentiating structures of the edge of the mantle.
Simpson in the diagnosis of a number of genera states that the edge of the mantle is "double." According to my observations, it is double along its whole extent in all forms. While the outer edge is closely adjacent to the margin of the hard shell, and is always simple, the inner edge, which is generally parallel and close to the outer edge, is more or less expansile, and is able to fill and close the gap between the two halves of the shell, when the adductor muscles relax, that is to say, when the shell "opens." And further, this inner edge of the mantle is not uniform in its structure all along its margin, but shows certain differentiating structures, some of which are systematically valuable.
What to read after A Monograph of the Najades of Pennsylvania Vol. 4 No. 6?
You can find similar books in the "Read Also" column, or choose other free books by Ortmann, A. E. (Arnold Edward), 1863-1927 to read onlineMoreLess
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