CLASSIFICATION OF THE PRIMORDIA 



99 



certain places we observe (on the hands of certain persons) 

 ribbon-like segments, which are divided themselves by slight 

 transverse furrows ^ into square segments or scales, x+2, which 

 correspond (mechanical concordance) to the scales of a lizard 

 or the unicellular seginents x + 2 in Fig. 9. When it happens 

 that two or three adjacent ribbon-Uke segments are divided 

 into square segments, the chess-board system becomes evident : 

 one might say that the epidermis consists of scales.^ In the 

 centre of each scale the opening of one gland is visible. 



Ordinarily, however, the slight transversal furrows are 

 obsolete, but the pores (openings of the glands) remain always 

 distinct, as vexUlary marks which indicate the latent segmenta- 

 tion : they may be counted (for instance, at 

 the finger-ends) and from their number we 

 know the number of amalgamated scales. 



SECOND EXAMPLE: It may happen 

 that the Umits between the segments of a 

 chess-board system are obsolete, but that the 

 segments differ from each other by one or 

 another property. In such cases the seg- 

 ments may be counted and their limits are 

 more or less (although indirectly) discernible. 

 The shell of many molluscs (for instance. 

 Cassis tessellata) is adorned with a regular 

 system of coloured spots in longitudinal and 

 transverse rows.^ These spots are vexillary fig. 12.— Portion of 

 marks which point to the existence of a human epidermis 

 chess-board system in one of the layers of f^^tH^'^J!^:^ 



the shell. scale a gland 



THIRD EXAMPLE : The curious square 

 spots which form a sort of checker-work in the epidermis of 

 the perianth of certain flowers {Fritillaria meleagris, certain 

 Colchicacea, Vanda ccerulea, etc.) have perhaps a similar 

 significance. 



REMARK : Between the examples mentioned or alluded to in §§ 80-81, 

 neither moiphological homology nor physiological analogy, nor phylogenetic 

 relations exist. They are all governed by the general principle 01 mechanical 

 concordance — just as deeply different chemical entities which crystallize in 

 the same system. 



1 To discern these slight furrows I have used a power of x 16. 



^ After desquamation, by which the corneous layer of the epidermis is carried 

 off, the longitudinal and the slight transversal furrows are reformed in the new 

 corneous layer exactly as they were before. From this it may be concluded that 

 the existence of the scales depends on a segmentation of the meristematic layer 

 (rete mucosum ) of the epidermis. 



^ Periclinal (EW) and anticlinal (NS) rows. These terms are used here with 

 reference to the margin (border) of the aperture of the shell. With regard to 

 the shell taken as a whole periclinal = longitudinal and anticlinal = transverse 

 (spiral). See p. 113. 



