PLATE III. 



Explanation of the letters used in the Plates. 



al Alimentary canal. 

 an Anus. 



hc^ Body-cavity of prsoral lobe. 

 hc^ Body-cavity of second region. 

 he'' Body-cavity of trunk. 

 bp Branchial plumes. 



hi Basement-tissue. 



ch Ciliated hypodermic organ. 

 cm Circular muscular coat. 

 cos Peculiar ciliated folds (sensory?). 



gbis Glandular organ at posterior end. 



hp Hypoderm. 



int Intestine. 



Im Longitudinal muscular fibres. 



linn Longitudinal muscular coat 



(somewhat peunate). 



m Mouth. 

 msv Ventral mesentery. 

 insd Dorsal mesentery. 



np Nephridia. 



ns Nerve-centre. 

 nt Nerve-cords. 

 m CEsophagus. 

 ov Ova. 

 r Uectum. 

 rm Radiate muscles. 

 vh Blood-vessels. 

 re Vascular spaces in region behind 



tentacles. 

 vt Stomach. 



Fig. 1. Longitudinal section through the base of the branchial tentacles and the anterior region 

 of the body. The funnel leading to the mouth is indicated at m ; a, the specially developed hypo- 

 dermic layer witli the somewhat free edge ; xh, the vessels at the bases of the various brancliial 

 ■whorls, which are arranged in series one above another ; ms, the special fan-like muscles which 

 act on the several whorls. The large amount of skeletogenous or basement-tissue in this section 

 is characteristic of the region. The section is slightly oblique, and thus the nephridial channel, np, 

 is very distinct. The space in which the folded mesenterial organ arises is marked cos, and the 

 continuation in the body-cavity, cos^ ; ch, the ciliated hypodermic organ; ce, cesophagus; 7;^, hypoderm 

 peculiarly folded. The bases of the whorls show thickened hypodermic patches with black 

 pigment. X 40 diam. 



Fig. 2. Transverse section of the central nervous system in a young example ; nc, finely 

 granular tissue, with a trace of fibres. X 210 diam. 



Fig. 3. Transverse section of the bases of the branchial fans, the great central muscles of which 

 are indicated by vie. The knife has passed through the ciliated hypodermic organs, ch, on each 

 side ; hp^, the median ventral or anterior hypoderm which at each side gradually merges into the 

 skeletal arches in connection with the branchial apparatus ; Jpf, the free margins of the two inner 

 (second) branchial series of the region, x 40 diam. 



Fig. 4. Transverse section of the body-wall towards the posterior end of the body, showing the 

 somewhat symmetrical disposition of the hypodermic tissue, the long gland-cells presenting a 

 slightly radiate arrangement towards the surface ; elm, decussation of the muscular layers of the 

 region, x 350 diam. 



Fig. 5. Vertical and nearly antero-posterior longitudinal section of a larval Phoronis from the 

 tentacles of its parent ; ain, central chamber (archenteron) ; &c\ body-cavity of the prteoral lobe 

 wliich forms an arch over the mouth ; hc^, a long slit, which may represent the body-cavity of the 

 trunk. The hypoderm is clearly outlined all over, x 350 diam. 



Fig. 6. Oblique section of au embryo, showing the apparently large size of the body-cavity of 

 the prseoral lobe, &c\ The archenteron is indicated at am, but no special differentiation yet exists, 

 since it is bounded only by the basement-tissue beneath the hypoderm. x 350 diam. 



