The Quantitative Method in Biology

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1919 edition. Excerpt: ...segment (idioblast) was accidental. In many cases, however, a differentiation may be regarded as a result of a gradation of a peculiar kind, and it may even be surmised that this is a general rule. iw'Vis In a typical example of gradation the variation-of a property p along an axis is gradual, without any sudden jump. I call this continuoui gradation. In the caracal Lair represented in Fig. 5 (p. 71, for instance, tie gra&anan of the priroordhrrn breadth of the ceili is contiinioras along tie axis. 1 Segmentation and differentiation, which are quite distinct notions, are sometimes confounded under the term differentiation. Instead of saying, for instance, that an antenna of a certain insect is differentiated into twelve joints, we ought to say... segmented... or... divided.... When, Od the contrary, a sadden change is observed in the value of / at a certain level of the axis, gradation is issamtirtuaui and produces differentiation EXAMPLE: An antenna of Ctrabus is: with regard to the exoskeleton (=cuticula)) a rrrriaTial system divided into eleven segments (articles).1 The gradation of the primandram Icrik of the segments may be described (in the majority of the species) in the following way: --Joint 1: long. 2: short. 3: long. 4: short 3-11: length decreasing gradually from 5 to 11. Here joint 2 is differentiated from 1 and 3. Between 3 and 4 the differentiation is very distinct in certain species, less distinct in others. From 5 to 11 the gradation is almost always continuous. Between typical continuous gradation and typical discontinuous gradation (differentiation) all possible transitions exist. In a chess-board system continuous gradation (Fig. 13, 2), typical differentiation and all possible...