THE BlONOMirS OF CONVOLUTA EOSCOFFENSIS. 431 



open, and was drawn on August 29tli. The weather on August 28th and 

 29lli was dull. The sketch sliows a mass of developing green cells, still, 

 however, all colourless, in the phagocjte {PUAG.) that guards the mouth ; 

 two colourless cells near the hinder end {C. G. C.) ; and a group of three more 

 advanced cells (C. G. C.) evidently arising by division. 



Fig. 17. — A specimen hatched from the same stock as Fig. 16, in darkness 

 and sterilised water. It was drawn on August 30tli, after exposure to day- 

 light for a ^ew hours, during which time but little direct sunlight was available. 

 It measured 0'39 mm. in length, and exhibited co'ourless predecessors of green 

 cells (C. G .C), remarkable nucleated structures (X) of unknown significance, 

 and one "pulsellum " {Puis.), tlie nature of which is still unknown in spite of 

 the work of Geddes, Delage, and ourselves. 



Fig. 18. — A specimen from the same stock, and hatched under the same 

 conditions as the two previous ones, but maintained in darkness till September 

 3rd. It now measured 0'5 mm. in length, but the only trace of its colourless 

 cells is to be seen in the aggregated fat {G. C. degeu.). The effect of starva- 

 tion is seen in the vacuolation of the gut (Vac). Several developing pulsellse 

 (Puis.) are present. The degeneration of developing green cells to mere 

 heaps of fat is also seen on PI. 30, fig. Ga. 



Fig. 19. — A specimen ••15 mm. long, hatched with parents in sea water in 

 tiie light of the laboratory. The figure shows many interesting points in the 

 development of the green cells. Three distinct forms occur: the ordinary 

 green cells (G. C), the colourless cells (C. G. C), and small yellowish bodies 

 (S. Q. C), which, as the side figures B and C suggest, are probably budded off 

 from the green cells. The tract of modified protoplasm that forms a phago- 

 cyte is here specially large, and within it several colourless and small yellow 

 cells occur. The retention of the colourless phase of the green cells is an 

 interesting feature. A, B, and C show other features in the structure of the 

 green cell (chloroplast and stigma, St.). 



Fig. 20.— a young Convoluta 745 mm. long, from the beach, which 

 shows the retention of the colourless cells {C. G. C.) and the gradual develop- 

 ment even at this comparatively late stage of the life-history of the chloro- 

 plasts. At the hinder end of the animal this process is evidently at work. 

 The stigmata {St.) were particularly clear iu the young green cells of this 

 specimen. 



Fig. 21. — Two colourless cells from a specimen 035 mm. long, hatched in 

 sea water September 10th, and drawn September 19th, 1902. The figures 

 show the variable form and extent of the leucoplast {Chi.), the nucleus, and 

 the refractive granules. 



