CELLULAR DEGENERATION AND FORMATION OF PIGMENT. 1'35 



EXPLANATION OF PLATE XII, 



Illustrating Dr. E. Warren's paper, '^ Observations on Cellular 

 Degeneration and the Formation of Pigment in certain 

 Hydroids." 



Lytocarpus filamentosus (Lain.). 



Fig. 1. — X 60. Photo-micrograph of two pinnae in a normal unpig- 

 mented condition. 



Fig. 2. — x 60. A pinna in a strongly pigmented state; tlie tissues 

 appear to be moribund. 



Fig 3. — x 60. A pigmented pinna with the tissues disintegrating. 



Thuiaria tubuliformis (M.-Turn.). 



Fig. 4. — x 40. Photo-mici'Ograph of a portion of main stem sliowing 

 the commencement of pigmentation in the ccenosarc. Note the leopard- 

 like spots. 



Fig. 5. — x 40. Specimen in an advanced stage of pigment-degenera- 

 tion. 



Sertiilaria operculata Linn. 



Fig. 6. — x 40. Photo-micrograph of a portion of a branch in an 

 unpigmented condition. 



Fig. 7. — X 40. Branch strongly pigmented, but the hydranths are 

 still alive with distended tentacles. 



Fig. 8. — x 40. Branch in an advanced stage of pigmentation. The 

 ccenosarc has divided transversely in three j)laces, but the hydranths are 

 alive and the tentacles are expanded. 



