ADVANCE IN LOWER PLANT AND ANIMAL FORMS 



PLATE LXIX 



[69 



PLATE LXVIII {continued) 



Fig. 25. — Portions of cytoblastema of Halichondria panicea containing amoebiform cytoblasts in various stages of development ; the 

 smaller ones originating from spornlar bodies, x 1500. 



Fig. 26. — Associated cytoblasts from Aplysilla sulfurea with alternate and interconnecting pseudopodia, x 400 (F. E. Schulze). These 

 cytoblasts remarkably resemble in their general appearance the multipolar ganglia found in the spinal cord of mammals (the Author). 



Fig, 27. — A group of metamorphosed collared monads presenting an amceboid aspect. 



PLATE LXIX 



This plate illustrates symmetric grouping and symmetric forms ; also the various phases through which zooids 

 and monads pass during their hfe histories. 



Fig. 1. — Spheroidal monad chamber or " anipuUaccous sac" of sponge {Halisarca Dujardinii, Johnston) as seen in optical section 

 without intersecting an afferent or efferent aperture, x 800. The introversion of this monad chamber produces a rosette or ordinary 

 swarm gemmule. Compare with Fig. 1.3. This figure affords a good example of concentric radiating arrangement (the Author). 



Fig. 2.— Six collared monads attached laterally from an " ampuUaceous sac " of the same sponge. These when isolated greatly 

 resemble the moniliforni colonies of the collared monad {Desmarella moniliformis) seen iit Fig. 24, x 1000. 



Fig. 3. — " AmpuUaceous sac " of same type seen in optical section and intersecting {vide arrows) an afferent and efferent aperture. 



Figs. 4, 5, 6, 7, 8, 9, 10, 11, and 12.— Progressive phases of development of an " ampuUaceous sac " by segmentation from a primitive 

 amceboid body, x 400. At Fig. 10 the segmented products resemble amoeboid corpuscles and have no flagellate appendages. At Fig. 

 12 (profile view of matured ampuUaceous sac) the same elements liave developed internally projecting flagella ; the characteristic 

 collars being absent. Enclosed cytoblasts are seen at a, h of Fig. 12. Fig. 11 affords a beautiful example of radiating arrangement 

 similar to what occurs in crvstals and flowers. The development here figured resembles in its main features that witnessed in the 

 segmentation of the impregnated ovum and the formation of the germinal membranes in the higher animals. It begins by a division 

 of the nucleus and the sarcode surrounding it (Dalton). 



VOL. I. Y 



