: i \\ \\ ION 01 N \ 



iistraU'> the p.uu of a single >c.;iiinit ol lli 



Tin- segmrntal tube ,. ,c:tion, hut the 



dilated ve-iele i> shewn into \\hirh tin- M-gm- ; 



taken frnn the region of the li<\- ']'<> the right is seen the <>\ 



of a segnicntal tube into tin- ' i m the segi. left the commenc- 



ing formation of. i meter, vide p. 50:. 



1 JL;. s. Longitudinal ami -ion through the posterior part of the 1. 



proper of an embryo of Scyllium canicula at a st. n N and O. Zciss A, 



ocul. :. 



Tin- Action shews the nearly complet ;i;hian bcxli- 



Fii;. 9. Longitudinal and vertical section through the anterior p.m of the kidney 

 jnoper of the same embryo as fig. 8. Zeiss A, ocul. 2. 



The figure illustrates the mode of growth of the developing ureters. 

 9 A. More highly magnified portion of ;! ction as fig. 9. 



Compare with transverse section fig. 4. 



Fig. 10. Longitudinal and vertical section through part of the \Volfiian body of 

 an embryo of Scyllium canicula at a stage bt IP. 



The section contains two examples of the budding out of the vesicle of a segmental 

 tube to form a Malpighian body in its own segment and to unite with the tubulus of 

 the preceding segment close to its opening into the \Yolman duct. 



EXPLANATION OF PLATh> M AM) :;,'. (VIII. p. 168.) 



PLATE 22. 



Fig. A. Section through the dor>al region of an embryo of Scyllium stf/lat 

 the rudiments of two visceral clefts. The section illustrates the general features at -a 

 period anterior to the appearance of the posterior nerve-roots. 



//<-. neural canal, nip. muscle-plate, ch. notochord. jr. subnotochordal rod. 

 ao. rudiment of dorsal aorta, so. somatopleure. sp, splanchnopleure. al. alimentary 

 tract. All the parts of the section except the spinal cord are drawn somewhat 

 diagrammatically. 



Figs. B I, B II, B in. Three sections of a /V/V//r//j-embryo. B I is through 

 the heart, B n through the anterior part of the dorsal region, and B ill through 

 a point slightly behind this. Drawn with a camera. (Zeiss CC, ocul. 3.) 



In B in there is visible a slight proliferation of celU fnnn the dorsal summit of the 

 neural canal. 



In B ii this proliferation definitely constitutes two dub-haped masses of cell* (/r), 

 both attached to the dorsal summit of the neural canal. The masses are the rudi- 

 ments of the posterior n 



1 The figures on these Plates give a fair general idea of the appearance presented by the 

 developing spinal nerves ; but the finer details of the original drawings have in several cases become 



lust in the process of copying. 



The figures which arc tinted represent srrtimi< of embryos hardened in osmic acid; those without 



colour sections of embryos hardened in 



