THE NATURE OF THE GENE 365 



general lines which such an interpretation can take. It may, on the one 

 handj be suggested that the individual genes have some internal spiral 

 arrangement (perhaps to be compared with the indications of spiral 

 structure in the molecules of proteins such as insuHn)^ and that this 

 determines the formation of the visible spirals; these would then be 

 expected to be consistent for considerable lengths of the chromosome. 

 Or, on the other hand, one may point out that any elongated body 

 consisting of fibres orientated parallel to its length tends to become a 

 spiral if its surface contracts; but in this case there are usually frequent 



Fig. 147. The Double Coil at Meiosis, according to Darlington. — A and B. Lightly 

 and heavily metaphase stained bivalents with chiasmata localized near the centro- 

 meres. C. A telophase bivalent, all in Fritillaria spp. 



(From Darlington.) 



reversals of the direction of coiling. In both cases the actual assumption 

 of the coil must be regarded as a response to changed environmental 

 conditions. 



There are two particular coiUng phenomena which seem to be gener- 

 ally agreed upon, and which seem likely to be of especial importance 

 for the theory of gene structure; though in neither case is their inter- 

 pretation easy. The first is the phenomenon which DarUngton has 

 spoken of as a "hysteresis," though this probably is a rather inappro- 

 priate name. At the end of a telophase, the chromosomes only partially 

 unwind their metaphase coils (p. 43), and they appear again in the 

 following prophase still with the remains of these coils. During the 

 prophase, these so-called "relic" coils become finally unwound (and 

 for a time the chromosomes, which have no room to He stretched 

 perfectly straight within the nuclear membrane, become thrown into 

 ^ Crowfoot et al., 1938. 



