176 AN INTRODUCTION TO THE STUDY OF FOSSILS 



the parenchyme, and through this parenchyme it is posteriorly 

 closely united with its neighbors. 



Reproduction. — Each new colony arises from a sexually 

 produced individual. The same zooid possesses both ovary 

 and testis formed from specially modified cells of the paren- 

 chyme. The spermatozoa move about in the coelome and there 

 fertilize the ova. The fertilized ovum passes into a rounded 

 outgrowth of the zooecium, which forms a sort of brood pouch 

 and there develops into the embryo. This escapes from the 

 parent body, becomes fixed by a sucker to some object, and as 

 the " primary zooid " secretes the first cup (protoecium) , and 

 subsequently gives rise asexually by budding to the new adult 

 branching colony. 



1. Examine a colony, noting its attachment, method of 

 branching, the individual cups, avicularia. 



2. Examine the mounted specimen under a compound micro- 

 scope, noting the U-shaped digestive canal, tentacles surrounding 

 mouth, chitinous cup. 



3. What is the habitat of Bugula ? 



4. How is it protected ? 



5. How does an individual get its food ? 



6. Describe the method by which the digested food reaches 

 all parts of the animal. 



7. How does it breathe? 



8. How are the individuals of a colony united ? 



9. Describe its method of reproduction. 



General Survey of Class Bryozoa 



Usually colonial and encrusting animals. A tentacle-bear- 

 ing ridge, lophophore, surrounds the mouth. An introvert 

 is usually present, and a U-shaped digestive tube. The two 

 sexes are commonly united in the same individual. The body 

 wall of each individual, called the zocecium, usually becomes 

 hard by means of horny or calcareous materials, forming an exo- 

 skeleton which persists after the death of the animal, and which 

 forms the only portion of the animal capable of being preserved 



