58 THE GERM-PLASM 



shown that the process takes place as follows: — the formation 

 of portions of the new alimentary canal begins in certain cells 

 which are separated by fairly regular intervals ; these then 

 spread until they come into contact with one another. The 

 idioplasm of the new intestinal cells is consequently only con- 

 tained in these formative cells, and it is natural to suppose that 

 each of them contains only one kind of determinant. 



The same appears to be the case with the hair of mammals. 

 Every hair does not possess a special determinant in the germ, 

 but more or less extensive regions of the hairy covering are 

 represented each by one determinant. These regions are not 

 large, as is shown by the stripes and spots on the coat of such 

 animals as the tiger and leopard. The recurrence in the son, 

 on exactly the same part of the head as in the parent, of an 

 abnormal tuft of white hair, has been observed in the human 

 subject. 



Similar hereditary parts or determinates may be observed in 

 butterflies, in which the colours on the wings often form very 

 complicated lines and spots of slight extent but of great con- 

 stancy. Such regions are often limited to quite a few scales 

 (cells) : Lycccna argiis, for instance, possesses a black spot on 

 a particular part of the anterior wing consisting of only ten 

 scales, while the surrounding parts are blue. In this case we 

 may therefore conclude that the black cells are represented in 

 the germ-plasm by at least one determinant. The determination 

 may possibly be carried out in still further detail in this instance, 

 and each cell in the black spot may be determined from the 

 germ onwards ; and possibly it is only the constant inter- 

 mingling of two hereditary tendencies in sexual reproduction, 

 and the consequent variability in the number of scales, which 

 prevents us from recognising the fact. We can at any rate, 

 however, find instances of the determination of sinde cells 

 in other species of animals. For example, in many Crusta- 

 ceans a number of sensory organs are situated on the anterior 

 antennae: each of these corresponds to one cell. The number, 

 position, and form of these ' olfactory ' setae is determined 

 exactly for each species. The Ostracod Cypris possesses only 

 one olfactory seta on each antennule, while in the common 

 fresh-water species of Gammarus^ there are about twenty of 

 these structures, each of which is separately attached to one of 

 the consecutive joints of the feeler. In many blind Crustaceans, 



