558 JOHNSON. 



EXPLANATION OF PLATE XXIV. 



All figures on this plate, except Fig. 29, illustrate the fission of 5. ceeruleiis. 



Fig. 26. Early stage, previous to formation of new mouth, and at beginning of 

 coalescence of meganucleus. Latero-dorsal aspect of extended specimen. From 

 life. Zeiss, y**^. 



Fig. 27. Later stage. New mouth (<)') has formed, and meganucleus {mgn.) 

 has divided and begun to elongate. Ventral aspect. The new contractile vacuole, 

 c. v}, has become abnormally enlarged. From life. Zeiss, y'g. 



Fig. 28. Same stage as Fig. 27, animal contracted. New adoral zone strongly 

 curved. Blue stripes crenated. Ventro-lateral aspect. From life. Zeiss, j\. 



Fig. 29. Newly-formed contractile vacuole of S. roeselii. Longitudinal optical 

 section, drawn from living animal. Zeiss, ^ . 



Fig. 30. Stage of fission a Uttle later than Figs. 27 and 28. The new zone is 

 bent sharply towards the left, at the point where the fission-line would afterwards 

 appear. Animal extended, latero-dorsal aspect. Drawn from life. Zeiss, ||. 



Fig. 31. Mid-dorsal portion of semi-contracted specimen, showing fission-line (/) 

 running from dorsal border of new zone {a. z}) around body to right. From life. 

 Zeiss, {|. 



Fig. 32. Fission-line at a little later stage than in Fig. 31. It runs above the 

 upper curve of the new zone, forming a conspicuous cleft. Hardened and fully- 

 contracted specimen, dorsal aspect. Zeiss, | = X 230. 



Figs. 33, 35-37- Later stages of fission, showing the process of constriction 

 and shaping of frontal field of proximal zooid. Ventral aspect. Fig. 33 in semi- 

 contracted state; the others fully extended. Drawn from life. Zeiss, •=[%. 



Fig. 34. Five stripes and portion of fission-line, showing that, in contracted 

 state, the stripes form an angle at the constriction-line. Picro-acetic, Delafield's 

 haematoxylin, clove-oil. Zeiss, g ^^ 



