161 



named end in fibre-like processes, which alone possess contractil- 

 ity and are thought by Kleinenberg to be motor-nerve endings. 

 These large cells, from combining the functions of muscle and 

 nerve, are termed " nervo-muscle cells." The little cavities be- 

 tween the large endodermal cells and the muscular layer which 

 lies next to the entoderm is filled with small cells and lasso- 

 cells, forming what Kleinenberg calls the interstitial tissue. From 

 this tissue are developed the eggs and spermatozoa. 



The organization of all the hydroids and even Lucernaria and 

 the larger jelly-fishes (Discophora) is based on the plan of the 

 Hydra. They all have a simple body-cavity, but no true alimen- 

 tary canal surrounded by a perivisceral cavity. This is the dis- 

 tinguishing character of the Coelenterates. In the jelly-fishes, the 

 often complicated water vascular system of canals are simply 

 passages leading out from the axial gastro-vascular cavity. If we 

 place a jelly fish in the same position as the Hydra, i.e.,. with the 

 tentacles directed upwards, the general homology between the 

 parts can be clearly traced. In the Hydroids, such as Sertularia, 

 etc., the ectoderm is surrounded by a chitinous sheath, secreted 

 from this layer. While in Hydra the young bud out from the side 

 of the body, in the Hydroids the young are developed on a sepa- 

 rate stalk from the barren or nutritive stalk or u zooid." The in- 

 dividual Hydroid is thus subdivided into a reproductive and a. 

 nutritive zooid. The reproductive zooids- seldom or never take in 

 food, but are nourished by the nutritive zooids,. the two zooids 

 being connected b} 7 a common creeping stem called the "coenosarc." 



The Anthozoa or sea anemones and coral polypes ditfer from 

 the Hydroids and Medusae in having the stomach open at the 

 bottom into a second and larger cavity communicating with the 

 radiating chambers. In the Ctenophora there is a decided ap- 

 proach in the complication of the body to the Echinoderms. The 

 radiated structure so clearly shown in the lower forms is here in 

 part subordinated to the bilateral arrangement of parts ; they 

 have a right side and a left side. They also differ, in the mouth 

 opening into a wide digestive cavity, enclosed between two vertr* 

 cal tubes, uniting at the end of the body, where the stomach forms 

 a reservoir for the gastro-vascular tubes ramifying throughout the 

 body. They move by a peculiar apparatus consisting of bands of 

 comb-like flappers. Not detaining the reader with a definition of 

 the subdivisions of the Coelenterates we shall be content, with 



