54 RAMBLES AND REVERIES. 



dophora. Other allied groups of Hydrozoa are the 

 sub-class Hydroida, of which Hydra and Sertularia 

 are known to every microscopist. The less known 

 snb-classes Siphonophora and Lucernarida, along 

 with the Hydrocorallinae or Millepores, leading 

 on to Corals, the latter, however, belonging to 

 Actinozoa, which with Hydrozoa make up the 

 sub-kingdom of Coelenterata. 



Although Graptolites have very little in common 

 with any of these groups, yet it will be easier to 

 convey an idea of what their structure probably 

 was by drawing attention to the familiar Sertularia 

 or Sea-fir. A representation of one of these, 

 Sertularia fusca, is given (Fig. 10). The entire 

 colony, or polypary, as it is called, is seen at a, being 

 in appearance very much like a plant, and, indeed, 

 is picked up on the sea shore by multitudes who 

 suppose it to be a seaweed. At b is a magnified 

 view of a portion of the colony, where the shape 

 of the cups or calycles can be more easily made 

 out. These caps or cells are inhabited by polypes 

 or lowly jelly-like creatures. The stem is horny 

 and hollow, giving off many horny branches. The 

 polypes are connected with each other and with the 

 polypary by a fleshy tissue called the ccenosarc 

 (common flesh), which runs through the hollow 

 stems of the colony or hydrosoma. Occasionally 

 there will be found on the branches of the polypary 

 little capsules, called gonothecae, which may be 

 seen by the naked eye, but must be magnified in 

 order to perceive their shape. These are concerned 

 in reproduction. The embryo emerges from these 



