A Monograph of the Free and Semi-Parasitic Copepoda of the British Islands (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. 1880. Excerpt: ... BRITISH COPEPODA. Section II.--Pcecilostoma, Thorell. Thoeell's division of the Copepoda into three groups, Gnathostoma, Poecilostoma, and Siphonostoma, the distinctions between which are found in the characters of the mouth-organs, is disapproved by Claus and some other authors, chiefly, as I understand them, on the ground of the gradual lapse of one series into the other rendering it impossible to draw perfect lines of demarcation, but partly, also, on the ground of a difference of interpretation of the homologies of some of the appendages. While differing from M. Thorell as to the nature of some of these organs, I myself think that his proposed division is a very natural one, the three groups presenting characters which, though differing in degree in various species, do point, on the whole, to habits of life very remarkably different, and deserving of expression in any natural classification. The three groups are defined by M. Thorell as follows: Series 1. Gnathostoma. Os mandibulis duabus libens tribusque paribus maxillarum instructum, siphone nullo. See p. 31, vol. i. Series 2. Pcecilostoma. Os mandibulis et siphone carens, maxillarum paribus 3--1 (--0) instruction. Series 3. Siphonostoma. Os in siphonem, mandibulas 2 plerumque includentem, productum, et maxillarum paribus 3--0 instructum. As regards the debateable anatomical points, it may be useful if I quote, in the first place, some remarks of M. Thorell, taken from a letter which he was good enough to address to me some few years ago--before the publication of Dr. Claus's 'Neue Beitrage zur Kenntniss parasitischer Copepoden.' M. Thorell writes as follows: --" You know, of course, that I have proposed to divide the Copepoda into three parallel series, Grnathostoma, Poecilostoma, and Siphonostoma, ...