959 
not correspond to the metamerism of the rest of the body, at the 
same time indicate the place, where, for the first time pigmentation 
appears in the skin. We find the first trace of pigmentation in the 
beginning of the high ridge on the scales. Here of course is the 
place of most intense growth. From that point, the pigment spreads 
over the rest of the scale, to proceed from there gradually over the 
surrounding scales. Here also, I was able to observe cell-streams 
in many young embryos, where the large ribbed scales were only 
slightly to be distinguished. The design on the medial line of the 
back has likewise no connection whatever with the metamerism 
of the body. It forms crescent-shaped spots, with the opening turned 
backwards; they are placed at more or less regular distances and 
point also to a rhythmical skin-growth, though up to the present 
moment, I was not able to find any cell-streams. 
At last I wish to point out some peculiarities which occur at the 
manifold transversal striping in the embryos of reptiles. It is well- 
known that Emer accepted the longitudinal striped design as the 
original one and not only in the case of reptiles, but he made a 
general rule of this principle. Whether this theory is probable 
or not, may be left aside here; but in any case the fact remains 
difficult to explain, that in a great number of embryos of lizards, 
serpents and crocodiles very distinct cross-stripes appear first, even 
with forms, showing longitudinal stripes in the adult. 
A number of embryos of Lygosoma olivaceum, collected partly by 
Dr. L. pr Bossy, partly by myself, were at my disposal. The whole 
of the trunk and the tail shows sharply marked, broad, dark, nearly 
black stripes, which alternate with comparatively narrow, white 
stripes, without pigment in the skin. In the first place, not the 
slightest coincidence is to be found between the extension of this 
stripe design and the metamerism of the rest of the body. The left 
and the right side are not symmetrical, so that it offen happens 
that a dark stripe meets a white one on the medial line of the 
back (Fig. 5). However it is well-known that this annot form an 
argument against the metameric origin of the design, as the meta- 
meric spinal nerves and the bloodvessels to the left and the right 
are not always symmetrical. But also the number of the stripes is 
different on the two sides of the body and the following peculiarity 
of this difference is of great importance. 
As is more than well-known, the embryos of all the reptiles 
lie more or less like a spiral in the egg and now one generally finds 
that the dark stripes become broader and split into two at their 
broadest point towards the convex side of the body, because at that 
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Proceedings Royal Acad. Amsterdam. Vol. XXII. 
