. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. SiaOocysts of Arenicola 09 become closed, either by apposition of its walls or by blocking of its lumen by granular substance secreted by the gland cells in the wall of the tube. A striking instance of this latter condition was exhibited hy a specimen from Trieste, in which each statocyst (Fig. 37 p.) con- tained about forty statoliths, approximately spherical, nearly uniform in diameter, and composed almost entirely of secreted clutinoid substance, there being in each only a small central " nu
. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. SiaOocysts of Arenicola 09 become closed, either by apposition of its walls or by blocking of its lumen by granular substance secreted by the gland cells in the wall of the tube. A striking instance of this latter condition was exhibited hy a specimen from Trieste, in which each statocyst (Fig. 37 p.) con- tained about forty statoliths, approximately spherical, nearly uniform in diameter, and composed almost entirely of secreted clutinoid substance, there being in each only a small central " ; The statocysts were completely shut oil from the exterior, the tube of each being closed by a plug of granular secretion. Similar conditions are met with in A. assimilis var. aj/inis. The statoliths of examples from Otago Harbour, New Zealand, are irregular bodies (Fig. 38 a) ; but those of specimens from near Wellington, New Zealand, from Tasmania antl from the Falkland Islands (Fig. 38 B), are rounded, each being composed of a central granule with a thick envelope of yellow secreted material.' The canal of the statocyst is moderately widely open throughout its length in the Otago examples, but in all the others is closed at one or more points, generally by small masses of secretion of the same refringent nature as that composing the statoliths. In each statocyst of tlie two Falkland specimens examined there are two statoliths larger than the rest. They were the first statoliths of the post-larval stage. These observations on A. marina and A. assimilis var. ajfinis indicate clearly that the nature of the statoliths depends on whether actual open communication M'ith the exterior is or is not maintained. The form of the statoliths in those species in wliich a canal leads from the statocyst is variahle, and is therefore a character of little value in systematic work. Only one statocyst of A. glacialis is availa])le for examination. The lumen of the tube which connect
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