W. R. Coe — Anatomy of Cerebratulus lacteus. 511 



Pigure 12. — Transverse section through the middle of the proboscis; co, co', dorsal 

 and ventral crosses of muscles. The epithelium (e) is thick and much folded. 

 The nerves have spread out to form a nerve-plexus {np) between the circular 

 and inner longitudinal muscular layers. The thin, outer circular layer {cm/) lies 

 immediately beneath the endothelium ; x 18. 



Figure 13. — Transverse section of the proboscis near its posterior end. The epithe- 

 lium (e) is very thick, while the two inner muscular layers are much reduced. 

 The nerve-plexus cannot be made out in this portion. The outer longitudinal 

 muscular layer (Im') remains comparatively strong; x 18. 



Plate XIII. 



Figure 1. — Diagram of the blood- vascular and nephridial systems. The two large cephalic 

 lacunae {cT) are united in front, above the rhynchodseum, by a small commissure {od). 

 The ventral commissure is much larger, and from it arise the buccal vessels (Jbh) 

 and the dorsal vessel {dh). The dorsal vessel passes backward within the pro- 

 boscis-sheath to the point x without branching. At this point, which is at the 

 posterior end of the oesophagal region, the vessel leaves the sheath and gives off a 

 pair of branches {av\ which anastomose with the lateral vessels {Iv) opposite each 

 pair of intestinal cseca. The nephridia occur in the middle portion of the 

 oesophagal region, and have a single pair of efferent ducts [ue). 



Figure 2. — Cells isolated from the intestinal epithelium by macerating in a dilute solu- 

 tion of formalin; 2a, a "goblet-cell" with its highly refractive secretion in small 

 particles ; 2c, more slender cells but having a similar secretion. In 2e the secretion 

 has collected into globules {s) of considerable size ; w, nucleus ; ud^ fibre-like process 

 which is attached to the basement membrane ; x 300. 



Figure 3. — Epithelium from the intestine of Micrura affinis. The slender cells are 

 partly filled with the characteristic colorless secretion in small globules ; x 150. 



Figure 4. — Epithelium from the oesophagus of Carinella. The ciliated cells are very 

 little elongated and among them are found many " goblet-cells " filled with a 

 mucus-like secretion ; x 150. 



Figure 5. — Diagram of a portion of the nephridial system as shown in figure 1, 

 enlarged. The nephridial canals {u) are cross-striped while the blood-vessels are 

 only outlined; Iv, lateral vessel with branches about the oesophagus. 



Figure 6. — Diagram of a portion of the nephridial and blood-vascular systems of 

 Lineus socialis. One main nephridial canal (w) with several efferent ducts {lie) is 

 seen close beside the lateral lacuna {II). There are few branches either from the 

 nephridial canals or from the lateral lacunse. 



Figure 7. — A portion of the vascular system in Cerebratulus Z^nd^MS from a horizontal 

 section. The nephridial canals break up into many small twigs {u) which wind 

 about on the outer border of the large, lateral blood-lacuna {U). 



Figure 8. — Longitudinal section of the efferent nephridial duct as it passes through the 

 body-wall. Neither the cell-walls nor the cilia could be made out. Beneath the 

 thin basement membrane is seen a thick layer of connective tissue (c) ; w, muscles 

 of the body-wall ; x 200. 



Figure 9. — Transverse section of the median, or dorsal, vessel showing the inner endo- 

 thelium {en') with the muscular coat (m) made up mostly of circular muscle-fibres ; 

 jpCy the thick layer of elongated parenchyma-cells, bordered on the outside by the 

 endothelium {en) of the proboscis-sheath ; x 50. 



