344 RANDOLPH. 



EXPLANATION OF PLATE IV. 



(Figs. 13, 14, IS, 17, 18, ig, 20. Lumbricuhis variegatus Grttbe. Figs. 16, 16 a. Lujnbrictis 

 clidus Hoffnt. {Allolobopkora /cetida Sav.).) 



Fig. 13. From a sagittal section of a slightly advanced stage, showing the connec- 

 tion of the developing neural cord with the ectoderm, x 300. 



Fig. 14. From a longitudinal vertical section of a more advanced specimen, showing 

 the fusion of the nephric foundation with the mesoderm. The plane of the section 

 is slightly oblique, passing at the right of the figure through the longitudinal muscles, 

 and at the middle and left through the centre of the foundation, x 520. 



Fig. 15. From the same series as in Figs. 7, 8,9, and 11, the seventh section 

 anterior to the one figured in 9, showing the double origin of the dorsal vessel, and 

 being an advance upon the condition shown in Fig. 6. x 520. 



Fig. 16. From a transverse section through the regenerating tail of Lumbricus 

 olidus, Hoffm. (^Allolobopkora fcciida, Sav.), showing mesodermic elements, lateral 

 and composite median, corresponding to those in Lumbriculus and consisting of 

 embryonic tissue which stains more deeply, and is therefore easily distinguishable 

 from the adult tissue with which it is surrounded. X 270. 



Fig. 16a:. The whole section of which Fig. 16 shows a more highly magnified 

 part. Immediately ventral to the new mesodermic tissue is a mass of deeply stained 

 cells which are in connection anteriorly with the ventral nerve cord, and posteriorly 

 with the new ectoderm ventral to the proctodeal invagination. The figure shows the 

 relatively small area occupied at first by the regenerated tissue and its position sur- 

 rounded by the adult tissues. The outlines were drawn with the camera and the 

 details are half schematic. X 60. 



Fig. 1 7. From a longitudinal vertical section of an early stage, stained with borax 

 carmine, and afterwards with picric acid dissolved in 70 per cent alcohol, showing 

 the beginning of the formation of the circular muscles. The figure is from a section 

 much thinner than the average (which is ^\-^ mm.), which makes it possible to see 

 the faint lines along which the fibrillce later separate. The dark -pointed tips repre- 

 sent the amount of elongation of the fibre in its long axis (around the body-wall of 

 the worm) on each side of the nucleus. X 450. 



Fig. 18. Showing a longitudinal vertical section from a regenerated tail about 

 two days old. The fibrillte have begun to separate from one another and from that 

 part of the peripheral layer of the fibre in contact with the ectoderm. X 450. 



Fig. 19. From a longitudinal vertical section of a specimen older than in Fig. 18, 

 showing a structure similar but more advanced. This is practically the adult condi- 

 tion which is generally obscured by the pressure of the longitudinal muscles. X 450. 



Fig. 20. From a longitudinal vertical section of a regenerated tail of four days' 

 growth. The section shows the ectodermic foundation lying still in the ectoderm, 

 and at the same time the circular muscles already formed both in the region of the 

 ectodermic foundation and far posterior to it where the ectoderm is still undiffer- 

 entiated. X 100. 



All the figures, except \ba, drawn with camera. 



