508 W. H. Coe — Aoicitomy of Gerehratiiliis lacteus. 



dn, dorsal, or median, nerve. mc, " median " cells of ciliated canal in 



e, epithelium ; integument. side-organ. 



e'm, epithelial musculature. mf, muscle-fiber. 



en, endothelium of rhynchocoelom. ml, median blood-lacuna. 



en\ endothelium of blood-vessels. n. nucleus. 



/", split between intestinal ca;cum and sur- n'p, nerve-plexus. 



rounding gelati%)us tissue. o, mouth. 



fc. fibrous core in dorsal brain-lobe. od, anterior commissure of cephalic lacunae. 

 fc\ fibrous core in ventral brain-lobe and oe, oesophagal epithelium. 



in side-organ. ol, oesophagal lacuna, 



/o, ovarian follicle. ov, oesophagal blood-vessel with contractile 

 ^, g'. gland-cell; glands. walls, as distinguished from a lacuna. 



gc, ganglion-cell. ov\ ovdm. 

 gc^^ ganglion-cell of first type. p, proboscis. 



g-c-, ganglion-cell of second type. j?;c, parenchyma-cell. 



gc^, ganglion-cell of third type. pi. cavity, or lumen, of proboscis. 



gd, gelatinous tissue. ^;w, proboscis-nerve. 

 gd\ genital duct. po, proboscis-opening. 

 gs, genital sac. ps. proboscis-sheath. 

 hm, horizontal muscles in the region of r, rhynchodaeum. 



the mouth. re. rhynchocoelom. 



«, intestine ; interstitial cells of body- rf^ radial fibres. 



epithelium. r/, fibres from ganglion-cells. 



«c, intestinal caecum. ro, rhabdite-like bodies. 



ie, intestinal epithelium. r<s, rhynchodaeum sphincter, 



y, zona pellucida. 5, secretion. 



hy "lateral" cell of ciliated canal in side- sc, sc\ sc'\ germinal epithelium. 



organ. sp, spermatozoa. 



Zc, lateral cord. tg^ tubular gland in cutis. 



II, lateral lacuna. %, nephridial canal. 



Z?n, longitudinal muscles : inner layer of we, efferent duct of same. ^ 



longitudinal muscles. ud, root-like process of epithelial cell. 



lm\ outer layer of longitudinal muscles. v, ventral brain-lobe. 



Is, lateral, or cephalic, slit. vc, ventral commissure of brain. 



Iv, lateral blood-vessel. vn, vagus nerve. 



on, muscles. x , point of attachment of proboscis. 



With the exception of Plate XIIT. figs. 3, 4, 6, 7, 10. and Plate XY, figs, 4, 5, 9, 

 11, 13, 14, all the figures are taken from Cerebratulus lacteus, 



Plate X. 



Figure 1. — Transverse section through the anterior portion of the head in front of the 

 brain. The large cephalic lacunae {el) are seen on each side of the rhynchodaeum 

 (r); X 8. 



Figure 2. — Transverse section through the head in the region of the brain-commis- 

 sures ; dc, dorsal commissure : vc, ventral commissure. The cephalic lacunae {cl) 

 are very small and compressed ; x 8. 



Figure 3. — Transverse section through the head in the region of the brain ; d, dorsal 

 brain-lobe; v, ventral brain-lobe; cc, canal leading to side-organ. The dorsal 

 blood-vessel is seen in the walls of the proboscis-sheath {ps)\ cl, cephalic lacuna ; 

 ml, median lacima ; x 8. 



