Plate VI. 



Synaptin^. 



Synaptula hydriformis (Lesueur). (Prom Clark, 1808a.) 



Figure 1. Segmenting egg; 33-cell stage. X 225. 



2. Blastula. X 225. 



3. Pentactula larva. X 225. 



4. Ten-tentacled young. X 23. 



5. Adult animal. Natural size. 



6. Adult, opened to show inner organt^. Natural size. 



7. Radial piece of calcareous ring. X 35. 



8. luterradial piece of calcareous ring. X 35. 



9 

 10 

 11 

 12 

 13 



b. From tentacles 



Stages of development of a piece of the calcareous ring. X 225. 

 Anchor. X 120. 

 Anchor-plate. X 120. 

 Anchor-plate. X 120. 

 Miliary granules. X 225. 



14. Calcareous rods. X 285. a. From around madrepore plate. 



of a 10-tentacled larva. 



15. Vertical section through eye-spot. X 950. 



16. Horizontal section through positional organs and nerve. X 500. 



17. Vertical section through a sense-jjapilla and its ganglion. X 500. 



18. Vertical section through base of a tentacle, to show arrangement of parts. X 35. 



19. Tentacle. X 22. 



20. Cross-section of young tentacle, to show separation of digit-canals from tentacle- 



canal. X 225. 



21. Cross-section of body-wall. X 80. 



22. Monstrous twin larva. X 225. 



The following explanatory letters are used on this plate: 



AO=atrial opening. 

 BV^l:>lood-vessel. 

 CF^=ciliated funnels. 

 CM=circular muscles. 

 CE=calcareous ring. 

 CT=connective tissue. 

 Cart. K.^cartilaginous ring 

 Cir. C.=circular canal. 

 Ect.=ectoderm. 

 Epid.=epiderjnis. 

 Epith.^^epithelium. 

 GG=genital gland. 

 ga.=ganglion. 

 LM=longitudinal muscles. 

 LGO=larval glandular organ. 

 M^mouth. 



Mes.^mesenchyme. 



My.=mesentery. 



NE=nerve ring. 



N=nerve. 



Oes. N.=oesophageal nerve. 



0=positional organs. 



PT^primary tentacle. 



I'V^polian vessels. 



HN=radial nerve. 



SC=stone canal. 



SO=secondary outgrowth of hydrocoel. 



TC^canal of tentacle. 



TN=tentacle nerve. 



TV=tentacle blood-vessel. 



V=valve. 



WP=water pore. 



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