The simple ascidians from the northeastern Pacific in the collection of the United States national museum

9781130312140: The simple ascidians from the northeastern Pacific in the collection of the United States national museum

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. 1913 Excerpt: ...was 142 mm. long in this individual. The gut of a dissected animal resembles that of a mouse quite as much as it does that of an ordinary ascidian. So far as I have been able to determine the canal of Styela nordensJcjoldi Michaelsen, 1900, from the region of Cape Horn, approaches that of this species more closely than any other. However, there is no such elaborate coiling of the organ in the South American species as in S. macrenteron, and there is little in common between the two species in other respects. Many of the individuals possess a stout, hard, sometimes quite regularly pyramidal spike or horn between the siphons (fig. 18). In this the species strongly resembles a Styela that has been known as S. monoceros because of this structure. There is, however, no possibility of identifying the animals before us with the S. monoceros of the north European seas. Herdman (1893), who considers monoceros to be a good species, has described and figured the animal, and the simplicity of the intestine as shown by him would of itself be nearly conclusive as to the specific distinctness of the two creatures. But as a matter of fact they differ to some extent in almost every respect, macrenteron being somewhat larger in size and more cylindric in form; having a larger number of tentacles, more internal vessels on the branchial sac, both on the folds and between them; more stigmata between the vessels, and, seemingly, a larger number of folds in the stomach wall. Hartmeyer, 1899 and 1903, has returned to the older vi w that monoceros is only a form of S. rustica, there occurring, according to him, horned individuals of rustica which are indistinguishable, specifically, in any other way from hornless animals. Not having had an opportunity to study the subject fir...

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