1 84 WORMS. 



DIAGRAM IX. 



Arenicola. 



Aren. I shows the external form, the tufts of setae, the thirteen gills. 

 The tail region is cut short. (After Cunningham and Ramage.) 



Arm. 2 shows a dissection of the anterior region ; paj). the papillae 

 on the proboscis, sept, three anterior mesenteries or septa, gP. s.'o.&gl^. 

 the glands of the gullet (g), neph. the nephridia, b. j. the sacs for the 

 bristles, n. the ventral nerve-cord, int. the beginning of the intestine, 

 ht. the heart. (After Vogt and Yung.) 



Nerve shows the anterior part of the nervous system ; cer. the cerebral 

 region, ot. the associated otocysts, proh. the relative position of the pro- 

 boscis, rg. the oesophageal ring, g. f. the position of the giant-fibres. 

 (After Vogt and Yung.) 



Sect. I shows a transverse section of a typical Polychsete ; the dotted 

 external line represents the epidermis, c. ?«. the circular muscles, /. m. 

 the longitudinal muscles, ». the ventral nerve-cord, t. m. transverse 

 muscles, rep. the position of the reproductive organs, neph. part of a 

 nephridium, g. the gut, d. v. the dorsal blood-vessel, neurop. the neuro- 

 podium, with ventral cirrus (v. c. ), notop. the notopodium with dorsal 

 cirrus {d. c), br. the branchiiE or gills. (After Lang. ) 



Sect. 2 shows a transverse section of Arenicola, showing the epidermis 

 (ep.), the muscles (m.), a nephridium {neph.), the gut (/.), a tuft of 

 bristles above the opening of the nephridium, n. the ventral nerve-cord, 

 and indications of the blood-vessels associated with gills and gut. 

 (After Cosmovici.) 



Larva A and B are developing trochospheres, in. is the mouth, ap. p. 

 the apical plate, mes. the beginning of mesoblastic segments, kn. an 

 anterior kidney-tube. The anterior ring of cilia, the curve of the food- 

 canal, and the growth and segmentation of the posterior region are 

 evident. (After Hatschek.) 



