30 ARKIV FÖR ZOOLOGI. BAND 13. N:0 25. 



than in the rhomboids, but their respective length is almost 

 the same, varying from 21 (i to 30,4 \i. 



The figures 1 to 10 on plate 3 represent typical digitiferous 

 crystals, drawn from the living. In most of them the rhomboid 

 system is well pronounced, though it has become somewhat 

 suppressed in, for inst., figs 8 and 9. Thus, issuing from the 

 rhomb or rhomboid as ground form, we observe that the full- 

 grown and most regular crystals have three or four digitiform 

 processes running out from the acute angles, but only two 

 from the obtuse ones. Not seldom some one or other of the 

 processes is bifurcate. However, it is to be noticed that irreg- 

 ular forms of this crystal type is very commonly met with. 

 Strangely enough, a certain symmetry predominates, the oppo- 

 site angles of the rhomboid presenting almost the same number 

 of processes and the same arrangement of them. When more 

 than one process shoot out from the obtuse angles, they seem 

 to issue from a common base, thus indicating the presence 

 of a single låter al process to be the primitive. 



A careful examination of fresh digitiferous crystals ex- 

 hibits that a web of clear plasma is expanded between the digits. 

 Furthermore, one discerns a central rounded nab, or frequently 

 a minute rhomboid kernel which, in its turn, can be environed 

 with a slightly larger and more irregular one (pl. 3, figs. 3 — 8, 

 10). Besides, in many instances we observe a sharply marked 

 rhomboid figure environed with a light, crenulate frame, and 

 traversed by an elongate, brilliant spool (pl. 3, fig. 1); in other 

 cases, the environed rhomboid presents a granular structure 

 and is bordered by strong dark lines which do not meet at the 

 acute angles (pl. 3, figs. 2 and 3). The nucleus, invisible 

 in fresh cells, appears very distinctly af ter fixation and staining 

 (pl. 3, figs. 17, 18 and 24). 



As to the development of the digitiferous crystals, I 

 suppose them to originate in amoeboid cells. In accounting 

 for this process and in order to be underst ood, I find myself 

 obliged to make use of such terms as »calcif ication » or »cal- 

 cified plasma». By that, I do not mean that the crystals 

 really are made up of, for inst., carbonate of lime or phos- 

 phate of lime etc; owing to my superficial knowledge of micro- 

 chemical researches, I am unable to entertain a proper idea 

 of this matter. I use the terms in question in order only to 

 give utterance to my thoughts. 



