Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 Excerpt: ... longer restricted by outside forces, starts its further development and becomes a functional opercular organ. However, it does not develop into an operculum of the simple type like the primary functional one. Instead it takes on the characters of the adult Hydroides operculum with two rows of serrations. Beside the inverted cone with serrations around its upper edge there is an additional circlet of pointed and often hooked processes, which constitute the most important character of the Hydroides group as distinguished from the Serpula group. At the same time the broken stump on the left side has started to develop a knob of embryonic tissue which grows only up to the stage represented by the rudimentary operculum of the adult and is in its turn restricted in its further development by some force most likely similar to the one which in the first place restricted the original primary rudimentary operculum. There are, therefore, at this time a secondary functional operculum on the right side and a secondary rudimentary operculum on the left side. These have the essential characters of the opercula of adult specimens of Hydroides. However, one point of difference is evident in specimens taken at random from the sea. It is found that approximately the same number have the operculum on the left side as on the right though there is uniformly a slight advantage in favor of the right-handed ones (57 per cent right-handed to 43 per cent left-handed in H. dianthus), while all the larvae appeared first as left-handed ones and later by reversal changed to right-handed ones. How does this change occur? Either we must suppose that the similarity in character of all the larvae was accidental or that the reversal takes place in nature during the life of the individual mor...
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