80 



LOWER INVERTEBRATES. 



ized, passes through the process of segmentation, a cavity appears within it, then it 

 assumes an elongated form, possesses a double wall about the central cavity, develops , 

 cilia upon the outer surface, and breaking through the containing 

 wall, escapes into the water where it leads a free life for a brief 

 time (see Fig. 67). Before long it enlarges at one end, settles down, 

 becomes attached by its larger end, loses its cilia, and proceeds to 

 develop a new colony of Eudendrium in the following way : It en- 

 larges at its free or distal end, and around this enlargement appear 

 a number of smaller swellings which develop into a wreath of ten- 

 tacles ; a mouth fonns in the extremity of the proboscis and a layer 

 of chitin is secreted around the body. Then by the simple pro- 

 cesses of growth, combined with budding, a new colony is formed 

 quite like the one from which the germ came. In this case the 

 medusa buds do not develop into free-swimming jelly-fishes, but 

 discharge their reproductive elements without leaving the parent 

 colony. 



Parypha crocea, a beautiful hydroid of a bright red or salmon 

 Fig. n.— Eudendrium color, is very common along the whole New England coast, while 



dispar, part of a fe- 

 male colony 

 medusoid buds 



mafe^'ooiony' with a closely related, if not identical species, extends southward as far 



as South Carolina. It attains a length, in favored localities, of five 

 or six inches, and grows in great luxuriance on the piles of wharves or 

 bridges, especially where the water is slightly brackish. The outer or 

 lower circle of tentacles are long, and just within them arise the medusae 

 buds resembling clusters of small, bright-red grapes. In each colony 

 the sexes are distinct, and in these buds the eggs or spermatozoa are 

 developed. The young escape in the actinula condition, and creep 

 about, finally attaching themselves, and then by budding and branch- 

 ing, large colonies are formted, which in turn produce medusa buds, 

 thus completing the life cycle. 



Another common form on our Atlantic coast from South Carolina 

 to the Gulf of Maine, is Pennaria tiarella. It grows in colonies equal 

 in size or a little lai-ger than those of Eudendrium, and is found at- 

 tached to rocks and eel grass, and often to floating algje. The zooids 

 are usually a roseate color, and the species is remarkable for its beauty. 

 In general structure Pennaria is like Eudendrium, but differs in hav- 

 ing, in addition to the one row of large tentacles, a number of smaller 

 capitate tentacles, arranged, more or less definitely in two circles near 

 the anterior end of the proboscis ; it also differs in its mode of branch- 

 ing, and in its method of reproduction. In the summer months there 

 may be found growing out of the lower part of the proboscis, one or 

 more oval bodies which finally develop a deep bell-shaped body with a 

 considerable opening at the free end, about which are a number of rudi- 

 mentary tentacles ; within the cavity of the bell-shaped zooid is a pro- 

 cess corresponding in shape and position with the clapper of a bell, it 

 is in fact the proboscis, and at its free end is the mouth. By means 

 of a sort of guUet or oesophagus passing through the proboscis, the 

 mouth communicates with the central digestive cavity located at the base of the pro- 

 boscis in the upper part of the umbrella ; from this central cavity four ducts at four 



Fig. 72. 



Paryplba 

 crocea^ natural 

 size. 



