134 INVERTEBRATE ZOOLOGY. 



tively ? Look along the edges at the bases of the zooecia, for little pairs of 

 jaws, something like birds' beaks, mounted on pedicles. These are the avic- 

 ularia, probably specialized individuals, fitted to detain and hold animals 

 which will attract the small forms upon which Bugula feeds. At the bases 

 of the separate zooecia are sometimes found oval cysts containing a single 

 egg. These are ooecia, which may be another specialized form, or have the 

 worth merely of a brood capsule. The animal itself bears a series of tenta- 

 cles, upon a semi-circular ridge, the lophophore. How many tentacles are 

 there ? They differ from those of hydroids in the presence of cilia and in the 

 absence of cnidoblasts. The alimentary canal consists of pharynx, stomach 

 vvdth a terminal coecuin, intestine and rectum.. As in most sessile forms the 

 canal curves back upon itself, the anus lying jiist outside the lophophore. A 

 muscular cord, the funiculus, extends from the coecum to the bottom of the 

 cup, probably to prevent over-extension of the parts. Ovaries develop on the 

 body-wall near the coecum. Testes appear upon the funiculus. The polyps 

 are hermaphroditic. 



I 08. Eor special examination of the skeleton, soak a colony in K-O-H, 

 wash in water and examine. This will bring out the details of the avicu- 

 laria, etc. 



Type XXII.— Asterias vulgaris. 



I 09. Collecting and preserving. This is the common star fish, abundant 

 everywhere at the sea-coast and obtained at low tide, especially about mussel- 

 beds and the piles of wharves. They are preserved for ordinary dissection by 

 being put alive into 95 ^, as they are poroxis enough to allow free entrance of 

 the fluid, and contain sufficient water to dilute the alcohol. For histology the 

 separate parts should be dissected out and preserved. 



I I O. External characteristics. Is the star-fish bilaterally symmetrical ? 

 How many planes will divide the animal symmetrically? Such a structure is 

 termed radiate. Upon what number is the radial symmetry based ? What is 

 the usual number among Cnidaria ? The body is divided into a central por- 

 tion or disc, and five triangular projections, the rays. The distinction be- 

 tween the two is slight here, but very definite in the " serpent-stars " (Ophiu- 

 ridea). Compare the two surfaces ; the flatter of the two is beneath when the 

 animal crawls, and has the mouth in its centre, and thus is called the oral 

 surface. The other is the ah-oral surface. Oral side;— Notice the central 

 mouth, its shape— very numerous soft tentacles, the amhtdacral feet, extend- 



