92 



MORPHOLOGICAL DEVELOPMENT. 



ther. Within the limits of the Jungermanniacece, we found 

 that while some genera exhibit this discontinuous develop- 

 ment, other genera exhibit a development that is similar to 

 it in all essential respects, save that it is continuous. And 

 here within the limits of the Hydrozoa, we find, along with 

 this genus in which the gemmiparous individuals are pre- 

 sently cast off, other genera in which they are not cast off, 

 but form a permanent aggregate of the third order. Figs. 

 149 and 150, exemplify these compound Hydrozoa — one of 

 them showing this mode of growth so carried out as to pro- 

 duce a single axis; and the other showing how, by repeti- 

 tions of the process, lateral axes are produced. Integrations 

 characterizing certain higher genera 

 of the Hydrozoa which swim or float 

 instead of being fixed, are indicated 

 by Figs. 151 and 152: the first of 

 them representing the type of a 

 group in which the polypes growing 

 from an axis, or ccenosarc, are drawn 

 through the water by the rhythmi- 

 cal contractions of the organs from 

 which they hang; and the second of 

 them representing a Physalia the 

 component polypes of which are 

 united into a cluster, attached to an 

 air-vessel. 



A parallel series of illustrations might be drawn from that 

 second division of the Cwlenterata, known as the Actinozoa. 

 Here, too, we have a group of species — the Sea-anemones — 

 the individuals of which, are solitary. Here, too, we have 

 agamogenetic multiplication : occasionally by gemmation, but 

 more frequently by that modified process called spontaneous 

 fission. And here, too, we have compound forms resulting 

 from the arrest of this spontaneous fission before it is com- 

 plete. To give examples is needless; since they would but 

 show, in more varied ways, the truth already made sufn- 



