100 SYNOPTIC COLLECTION. 



swimming individuals." The adult Acaulis (figs. 2, 3) is 

 attached by its base. 



Among the Tubularians there are some species which 

 develop free medusae, while others are more or less 

 reduced. In this group the zoons are at the ends of long 

 tubes, and those with the reproductive function are some- 

 times in the form of clusters of grapes^. 



Corymorpha nutans Sars (No. 118), is a solitary Tubu- 

 larian. The natural size is represented at the left, while 

 just back of it is the same greatly enlarged. At its base 

 are many thread-like organs for anchoring the animal in 

 the sand. A number of short tentacles are seen around 

 the mouth, and farther down there is another circlet of 

 much longer feelers. Between these two sets of tentacles 

 are the medusae buds. These have only one tentacle 

 when young and attached and also when mature and free 

 (No. 1 1 8, at the right). This model clearly shows the 

 four radiating canals and the manubrium. 



In Turritopsis (No. 119) we have a greater complexity 

 of the hydroid stage than that previously described. The 

 free-swimming embryo does not grow into a hydra, but, 

 spreading out more or less like a root, attaches itself and 

 buds forth hydras. In this way a colony arises. The 

 hydras in their turn bud medusae which swim away. 

 Here we have a modification of the phenomenon of alter- 

 nation of generations and a root-like form existing between 

 the parenchymella and the hydroid stage. 



The life history of Podocoryne is especially interesting. 

 It begins its existence as a hydroid, then forms a colony 

 by budding, and puts forth secondary buds in the form 

 of medusae. These swim away, but after a time they 

 take on reduced characters. The veil disappears, the bell 

 is reversed, shrunken to a shapeless mass, and turned 

 back with the tentacles (PI. 120). The eggs are seen in 

 the walls of the manubrium which hangs down below the 

 shrunken bell. 



This figure is instructive as showing the difference 



