Studies in Biology from the Biological Departments of the Owens College Volume 4 (Paperback)

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. 1899 Excerpt: ...form differs from that of Phyllodoce found so commonly in early spring. It has generally been assumed that the number of nephridia and gonads occurring in Arenicola marina is typical or fairly typical of the genus, and it is usually stated that the number of both these organs is a small one (five or six). An investigation of several other species of Arenicola, the results of which we hope shortly to publish in full, have shown that A. Grubii and A. Claparidii have five pairs of nephridia, and apparently the same number of gonads, whereas A. ecaudata has no less than thirteen pairs of nephridia, twelve of which bear large and complicated gonads of a size and complexity which is scarcely equalled by any other Polychset. What relations exist between A. marima and the other species of the genus cannot be discussed here, but it may be stated generally that the genus exhibits greater variety in the development of several systems of organs than has been hitherto suspected, and that it is no longer possible to exemplify the characters of Arenicola as a genus by using their particular grade of development in A. marina as a type. 12. General Summary. The following is a recapitulation of the new points which we have found in Arenicola marina. 1. On the Lancashire coast, and probably elsewhere, two well-marked varieties of Arenicola marina occur, differing, as the following table shows, in general appearance, in their habits, in the structure of their gills, and periods of maturity. 2. The cilia lining the central or gastric region of the alimentary canal are specially arranged (1) on the sides of a ventral groove which is continued to the anus, and (2) on curved shallow grooves running downwards and backwards into the former. The current caused by the action of these ...