PLATE XLIV 



Ccphalodiscus nigrescens, Lankester 



Figs. I, 2. Transverse sections of a young C. nigrescens passing re- 

 spectively through the collar and trunk-region. 



Fig. 3. Frontal section of a young C. nigrescens slightly older than the 

 one represented in Figs. 1,2, showing the growth of paired arms and the 

 relations of the heart and pericardium. 

 Fig. 4. Sagittal section of a young bud. 



Figs. 5, 6, 7. Drawings from whole mounts of three stages in the de- 

 velopment of the bud. 



a, proboscis; b, main ganglion; cc, collar cavities; d, notochord;/, 

 stomach;^, intestine; h, pharynx; Ai, heart ;y, pericardium; mcp, meso- 

 dermal cells in the proboscis cavity forming muscular strands ; ms, mass 

 of mesoderm in the trunk cavity of the bud, derived from the stolon of 

 the mother zooid; n, primitive gut; pc, proboscis cavity; pg, pigment 

 granules ; pi, posterior lobe of the proboscis ; pni, nerve plexus in the 

 ventral wall of the proboscis; ra, first pair of arms; rl, red line in the 

 proboscis ; rp, rudiments of the paired arms ; st, stalk with which the bud 

 is attached to the stolon of the mother zooid ; tc, trunk cavity ; tr, trunk- 

 region of the bud; vp, ventral part of the trunk cavity with clusters of 

 mesodermal cells enlarging to form the stolon. 



