222 H. D. Senior. 



Fig. 8.— Series 14567, section 39. 



Fig. 9. — From the reconstruction used for Fig. 12. 



Fig. 10.— From series 14G67 ; lOB section 70, lOD 79. 



Fig. 11.— Reconstruction 15011, from series 14670, sections 68 to 110; IIC 

 section 79. 



Fig. 12.— Reconstruction 15012, from series 14668, sections 39 to 09; 12C 

 section 54. 



Fig. 13. — Reconstruction 15013, from series 14071, sections 21 to 80. 



Fig. 14. — Diagram from the reconstruction used for Fig. 13 



Fig. 15. — Diagram from reconstruction 15014, from series 14672, sections 23 

 to 61. 



Fig. 16. — Reconstruction 15015, from series 14568, sections 20 to 56. 



Fig. 17. — Fig. 1 repeated. 



Fig. 18. — Series 1427.5, section 126. 



Fig. 19.— Series 14275, section 130. 



Fig. 20.— Series 14275, section 133. 



Fig. 21. — Series 14275, section 136. 



Fig. 22. — Reconstruction 14507, from series 14538, sections 82 to 136. 



Fig, 28.— Series 14538, section 128. 



Fig. 24.— Series 14538, section 132. 



Fig. 25.— Series 14538, section 140. 



Fig. 26.— Series 15002, section 138. 



Fig. 27.— Series 15002, section 148. 



Development of the Heart. 

 The process of development of the heart in shad may conveniently 

 be divided into four periods as follows : 



1. Formation of the heart anlage. 



2. Lasting until rhythmical contraction begins in the partially 

 formed heart-tube. 



3. In which the heart-tnbe is completed to form conus, ventricle 

 and atrinm, and assumes the adult position. 



4. Formation of the sinus venosus and hepatic vein. 



PERIOD I. formation OF THE HEART ANLAGE. 



The myo-epicardium and the parietal pericardium are developed 

 from the lateral plates of the mesoderm. That the endocardium is 

 derived from mesoderm, and from mesoderm alone, has already been 



