96 



THE PLANARIAN 



of the Turhellarial Put a small specimen on a slide under a cover 

 glass and examine for cilia. Are they uniformly distributed? Can 

 you detect flickering movements within the animal? These indicate 

 the position of the flame cells, which are excretory in function. Do 

 you find ducts leading from them to the outside? Draw (X 10), 

 showing the features observed. 



(d) Stained cross sections must be studied to make out the cellu- 

 lar structure. The outermost layer of cuboidal cells is the epidermis, 



Fig. 46. — Locomotion in planarians. A, ventral surface of animal showing 

 distribution of cilia; arrows indicate direction of ciliary currents; B. mecha- 

 nism of gliding movement; a, planarian seen from side; b, layer of mucus 

 (thickness exaggerated) secreted by animal; c, cilia; d, substrate; the arrow 

 indicates the direction in which the organism is moving. 



(From R. Pearl, 1903, Quarterly Jour. Microscopical Science, vol. 46.) 



or ectodermal epithelium. To what layer of the hydra does it cor- 

 respond? To what layer in the frog? The gut wall is composed of an 

 endodermal epithelium made up of large columnar cells. Are they 

 vacuolated? The region between the gut and epidermis is seen to be 

 composed of a syncytium of stellate cells which contains spindle- 

 shaped cells, the formative cells, and which is traversed by muscle 

 cells. Small oval or rodlike structures, the rhabdites, may be seen in 

 the peripheral regions of the syncytium and in the epidermis. The 

 nerve cords wall be seen on each side in the ventral region. Make a 

 figure to show the regions as observed with the low-power objective. 

 Draw under the high-power objective (2 X projected size) to show 

 the cellular structure of a narrow strip from the gut cavity to the 

 outside. Label in such a way as to indicate the functions of all parts. 

 What advance in cell specialization does the planarian show over the 

 hydra? 



Exercise 3. — Regeneration, Reproduction, and Development, 

 (e) Using a sharp scalpel cut a specimen into two or three pieces. 

 Keep the pieces in a wide-mouth bottle in some of the water in which 



