606 E. W. WACBKlDfc;. 



Fig. 4G. — Longitudinal frontal section tlirougli a larva of about the same 

 a"-e as tliat shown in figs, ii and i5. Picked out of Plankton. The epineural 

 folds (ep.) arc shown; these roof over the ambulacral grooves (i. e. the sur- 

 faces of the primary lobes of the hydroccele) and give rise to the epineural 

 canals. X 250. 



PiR, 47. — Longitudinal frontal section of a larva picked out of Plankton in 

 the second stage of metamorphosis. The opening of the stone-canal into the 

 water-vascular ring is shown; the pore-canal is indicated by dotted lines, as it 

 does not lie in the plane of the section. The evagination of the left posterior 

 coelom to form the dorsal canal of the fourth arm is shown (arm IV). x 250. 



Pig. 48. — Longitudinal frontal section of a larva picked out of Plankton in 

 the third and final stage of metamorphosis, a. I. Disappearing remnants of the 

 anlero-lateral arms. p. d. Remnant of right postero-dorsal arms. peri. Peri-oral 

 coelom originating as an outgrowth from the left posterior ccelom. muse. 

 Muscles originating from dorsal canal (arm-ca'lom) of arms IV and V. 

 X 250. 



Fig. 49. — Portion of a longitudinal frontal section of a larva picked out of 

 Plankton in the first stage of metamorphosis, ph. 4. 5. A perihaemal rudiment 

 showing its origin as an evagination of the left posterior ccelom. st. Stomach. 

 X 400. 



Pig. 50. — Portion of a longitudinal frontal section of a larva picked out of 

 Plankton in the second stage of metamorphosis, ep. s. Epineural canals, muse. 

 Muscular cells originating from the walls of the periluxmal space {ph. 3. 4.). 

 n. c. Ganglion cells originating from the ectodermic wall of the C()ineural canal. 

 n.'c' Ganglion cells originating from the wall of the periligemal space. «./. First 

 nerve-fibres. ;;. /. Postero-lateral arm cut obliquely. X 466. 



Fig. 51. — Sagittal longitudinal section of a larva picked out of Plankton 

 in the third stage of metamorphosis, gen. Primitive germ-cells originating 

 from the wall of the left posterior ccelom. X 233. 



Fig. 52.— Sagittal section through a young Amphiura squamata "25 mm. 

 in diameter taken from the maternal brood-pouch, muse. Muscular fibres 

 devcloi)ing from the cells lining a tentacle, gen. Primitive germ-cells forming 

 a swelling, which is the beginning of the genital racliis. x 233. 



F'lo. 53. — Longitudinal frontal section through an abnormal larva of 

 0|)hiothrix fragilis in the second stage of metamorphosis picked out of 

 Plankton. 1', 2', 3', 4', 5'. Lobes of abnormally developed right hydroccele. 

 X 173. 



