496 



EVOLUTION OF ANIMALS 



Part V 



sticky 

 granule 



Nucleus of cell 

 bearing granules 



Spiral elastic 

 filament 



Straight 

 filament 



Attachment to 

 core of tentacle 



B c 



Fig. 24.3. Adhesive cells: these sticky "lasso cells" compose a large part of the 

 epidermis of the tentacles. Still attached to the tentacle by the lasso threads they 

 are thrown against unfortunate little animals that are then stuck fast to them. When 

 the tentacle has collected its prey, it contracts and wipes itself across the expectant 

 mouth of its owner. A, a section through one of the branches of a tentacle (Fig. 

 24.1.). The outer surface is covered with the sticky heads of the "lasso cells." 

 Each cell is attached by a coiled filament which acts as a spring preventing the cell 

 from being wrenched off by the struggling victim. B and C, sticky cells with fila- 

 ments uncoiled and coiled. (B and C, redrawn after Wolcott: Animal Biology, 

 ed. 3. New York, McGraw-Hill Book Co., 1946.) 



pot (Fig. 24.3). Each cell discharges a sticky secretion. It is fastened to the 

 tentacle by a coiled contractile fiber encircling a straight fiber which acts as a 

 special holdfast while the contractile one is stretched out into the water. The 

 core of the tentacle contains a central strand of nervous tissue concerned with 

 the responses in the tentacle and a cord of muscular cells which provides for its 

 extreme contractility. As in coelenterates, the extensive branched enteron pro- 

 vides for digestion, absorption and transport of food, water, and metabolic 

 waste. The only opening in the enteron is the mouth which leads into a 



