Archive image from page 793 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 778 CRUSTACEA. this, striae are observed to appear, which are the rudiments of the branchial filaments. During this interval the thoracic extremities have become developed, and above their bases other branchiae have made their appearance, presenting in the beginning the form of tuber- cles, and subsequently that of stilets; smooth and rounded on their surface, but by-and-by becoming covered with a multitude of small tuberculations, which by their elongation ar
Archive image from page 793 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 778 CRUSTACEA. this, striae are observed to appear, which are the rudiments of the branchial filaments. During this interval the thoracic extremities have become developed, and above their bases other branchiae have made their appearance, presenting in the beginning the form of tuber- cles, and subsequently that of stilets; smooth and rounded on their surface, but by-and-by becoming covered with a multitude of small tuberculations, which by their elongation are gradually converted into branchial filaments similar to the preceding. During this period of the development of the branchiae these organs are applied like the extremities to the inferior surface of the embryo; but they sub- sequently rise against the lateral parts of the thorax, become lodged within a cavity situated under the carapace, and thus are no longer visible externally. The cavity destined to protect in this manner the branchial apparatus, is neither more nor less than an internal fold of the common tegu- mentary membrane. It shows itself first under the guise of a narrow groove or furrow, which runs along the lateral parts of the thorax below the edge of the lateral piece of the carapace. This longitudinal furrow is not long of expand- ing, and becomes consolidated by its superior edge with the internal surface of the carapace, which, by being prolonged inferiorly, consti- tutes the external wall of a cavity, the opening of which, situated above the base of the extremities, becomes more and more contracted, and ends by being almost entirely closed. The space in this way circumscribed encloses the branchiae, and constitutes what is called the respiratory cavity of the Decapod Crustaceans. From what has just been said, it would ap- pear that the embryo of the Astacus fluviatilis presents four principal periods with reference to the state of the respiratory apparatu
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