ADVANCE IN LOWER PLANT AND ANIMAL FORMS 



PLATE LXVI 



165 



PLATE LXVI 



This plate deals with Zooids ; with symmetry and asymmetry ; with radiating and concentric arrangements ; 

 with centripetal and centrifugal movements ; with amcBboid forms as the result of retrogression ; with growth, 

 force, &c. 



Fig. 1. — Spheroidal colony-stock of adult zooids {Ma;ioqjliizra planida), x 240 (Haeckel). This figure presents the general 

 appearance of hexagonal liver cell, pigment cells, epithelial cells, honeycomb cells, &c. 



Fig. 2. — Ideal section of same showing symmetrical cluster of zooids, resembling a flower in appearance. 



Fig. .3. — A single isolated zooid from same, composed of bell-shaped body, with cilia, nucleus (»), and contractile vesicle (cv). The 

 cilia are important alike for movement and fur securing food. 



Fig. 4. — A similar zooid having assumed an anitclwid phase (Haeckel). Shows retrogression and reversion of zooid to a 

 primitive, simple condition for reproductive purpo-ses analogous to the fusion of the simple male and female elements (ova and 

 spermatozoids) in the higher animals. 



Figs. 5 and 6. — Encysted zooids (Haeckel). Fig. .'5 shows radiating and concentric arrangements. Fig. 6 has divided by 

 segmentation into four spheroidal spornlar bodies. The encysting and disintegrating or breaking-up processes in zooids mark 

 important reproductive changes similar to what occur in insects (pupa state) and the segmentation of the yolk in vertebrates. 



Fig. '7.— Zooid {Actinomoyias pusilla) attached by single stalk-like filament, x 800 (W. S. Kent). 



Fig. 8. — Zooid (Adinomonas pusilla) attached by a number of ray-like pseudopodia. Figs. 7 and 8 illustrate the principle of 

 radiation in rudimentary animals. The power possessed by zooids of extruding and withdrawing their sarcode by centrifugal and 

 centripetal movements, as witnessed in pseudopoffia, furnishes the key to muscular and other movements in the higher animals. The 

 movements in question are fundamental. They are direct, pushing, or elongating, and pulling or shortening movements. They imply 

 no increase or diminution in bulk, and cannot be referred to elasticity. Both movements are vital in their nature. 



Fig. 9.— Animalcule {Rhimmonas verrucosa) enclosed within granular gelatinous sheath, x 750 (W. S. Kent). 



Fig. 10. — Animalcule {Rhizomonas verrucosa) devoid of such sheath. 



