PLATE I. 



al Alimentary canal. 

 a7i Anus. 



6c' Body-cavity of prreoral lobe, 

 ftc* Body-cavity of second region. 

 Ac' Body-cavity of trunk. 

 hp Branchial plumes. 



bt Basement-tissue. 



cb Ciliated hypodermic organ. 

 cm Circular muscular coat. 

 eos Peculiar ciliated folds (sensory 1 



Explanation of the letters used in the Plates. 



gbs Glandular organ at posterior end. 



hp Hypoderm. 



int Intestine. 



Im Longitudinal muscular fibres. 

 Ip7n Longitudinal muscular coat 

 (somewhat pennate). 

 m Mouth. 

 msn Ventral mesentery. 

 mM Dorsal mesentery. 



np Nephridia. 



?!^ Nerve-centre. 

 nt Nerve-cords. 

 ce (Esophagus. 

 ov Ova. 

 r Rectum. 

 rm Radiate muscles. 

 vb Blood-vessels, 

 re A'ascular spaces in region behind 



tentacles. 

 vt Stomach. 



Fig. 1. Outline of Phoronis buskii from the posterior aspect, that is, with the split between the 



Enlarcjed about four times. 



branchial fans and the anal region facing the observer, 



Fig. 2. Opposite aspect of the anterior end of the same form, which in this case shows two 

 Similarly enlarged. 



longitudinal grooves, 



Fig. 3. Transverse section of the anterior region of the body — in the region of the rectum, and 

 with the lateral vascular spaces, vc, which may represent the collar-cavities, still present. The 

 ciliated thickenings on the mesenterial wall are seen at cos, and the nephridial channel just before 

 it ceases at np. x 40 diam. 



Fig. 4. Transverse section of the anterior region of the body behind the former, and after the 

 parts have assumed the typical condition, with the somewhat pennate longitudinal muscular bands. 

 The intestine at this part is empty, and has assumed its usual triradiate aspect, the mesentery, 

 msd, fixing it dorsally and ventrally and also on the right. The peculiar ciliated fold of the other 

 (left) mesentery is seen at cos. The large median and lateral (right) blood-vessels are cut at vb ; 

 and one of the anastomatic branches at vh^ ; msv, the ventral mesentery. X 40 diam. 



Fig. 5. More highly magnified view of a portion of the body-wall in the same region. The 

 hypoderm, hio, has a pale cuticular margin, and abuts on the basement-tissue. It ; cm, circular 

 muscular coat ; Ipm, foliate or penniform arrangement of the longitudinal muscular fasciculi, 

 with basal processes, and intermediate connective-tissue and radiate muscular strands, rwi. x 350. 



Fig. 6. Transverse section of the body- wall near the posterior end. The peculiar arrangement 

 of the longitudinal fibres just inside the basement-tissue is shown at Im, spaces, moreover, occurring 

 within these, apparently from contraction of the circular fibres and basement-tissue. Within the 

 circular coat {cm) is a granular endothelium or a modification of this coat. 



Fig. 7. Section of a branchial tentacle with the hypoderm less developed than in the following. 



Fig. 8. Section of a branchial tentacle in which the hypoderm completely surrounds the base- 

 ment-tissue, and has long cilia on its broad edge. 



