EXPLANATIO.\ OF PLATE VI. 



EUNICE A MURICATA. HISTOLOGY. 



Fig. 



Fiu. 



¥ui. 



Fig. 



Fig. 

 Fig. 



Fig. 



Fig. 



I^IG. 



1. Transverse section of polyp across refracted tentacles: .a, a, a, bods' 

 wall; b, b, b, mesenteries; c, c, papillje of tentacles; e, e, e, ectodermal 

 investment of tentacles. 



2. Transverse section across gullet of polyp : a, a, a, mesodermal plates of 

 mesenteries; b, b, b, muscle fibres of retractor muscles; c, ectodermal 

 lining of gullet; d, d, muscles of gullet wall; e, e, cavity of gullet. 



3. Section throtigh convoluted xvall of gullet, greatly magnified : a, endo- 

 dermal cells; b, b, columnar ectodermal cells lining gullet; c, c, large 

 polar cells supposed to be nerve cells; d, d, mesodermal cells with 

 large nuclei. 



4. Lo7igitudinal section of polyp : a, a, a, retractor muscles; b, b, b, ten- 

 tacular muscles; c, c, c, retracted tentacles; d, d, tentacular papilla-; 

 e, e, convolutions of gullet; f, f, gullet wall; g, gullet cavity; h, h, 

 mesenterial filaments; i, i, ova. 



5. Large ovum, segmented: a, vitelline membrane; b. segmented mass. 



6. Ovum, unsegmented : a, vitelline membrane; b, granular protoplasm; 

 c, germinal vesicle; d, germinal dot; e, nucleated cells surrounding 

 ovum. 



Group of ova, the largest of xvhich has three germinal dots. Letters as 



I fig. 6. 



Ovum. Letters as in fig. 6. 



Fig. 10 

 Fig. 



Fk;. 12. 



Ovum in vjhich the protoplasmic mass has shrunk aivay from the vitelline 

 membrane 



Tiuo ova attached to pedicels, e, e. Other letters as in fig. 6. 



Part of mesenterial filament highly magnified : a, cells having small 

 nuclei, forming mass of filament; b, b, cells having large nuclei, 

 forming horse-shoe-shaped projections. 



Advanced ovnm or voung planula: a, ectoderm or epiblast; b, endo- 

 derm or hypoblast; c, germinal vesicle; d, germinal dot. 



