64 ZOOLOGY, 



about like the Aurelia by alternate contractions and expan- 

 sions of the umbrella. We will now enter into a more com- 

 plete account of this group based on Clark's characteriza- 

 tion. The disk is more or less octagonal or circular, um- 

 brella, funnel or urn-shaped, the end opposite the mouth 

 ending in a pedicel, by which it is attached temporarily to 

 sea- weeds. The mouth js square, and between the ectoderm 

 and endoderm is a jelly-like layer constituting the musculo- 

 gelatiniform layer (mesoderm) much as in Aurelia. This 

 layer extends into the tentacles and marginal anchors, as 

 well as into the pedicel. The cavity of the disk is divided into 

 four quadrant chambers, separated by as many partitions, 

 which extend from the mouth into the lobes nearly to the 

 margin between the tentacles. The latter are arranged in 

 eight groups or tufts just within the margin of the disk, at 

 eight points, which alternate with the foiir partitions and 

 the four corners of the mouth. The tentacles are hollow, 

 opening into the radial canals of the general cavity of the 

 body, and end in a globular or spheroidal expansion, serv- 

 ing as an organ of touch or prehension. In some forms, as 

 Halidystus auricula Clark, marginal anchors are situated 

 at eight points, exactly opposite the four partitions and the 

 four corners of the mouth ; they are originally tentaculif orm, 

 but in adult life form organs by which they adhere to or 

 pull themselves from place to place. The sexes are distinct, 

 the reproductive glands having the same position in each 

 sex. Nothing is absolutely known of the mode of growth 

 of these animals, but development is supposed to be direct. 

 Our common Lucernarian is Halidystus auricula Clark. 

 Its umbrella-shaped disk is an inch in diameter ; including 

 the tentacles, an inch and a half ; the pedicel half an inch 

 long. It ranges from Cape Cod to Greenland and south- 

 ward to the coast of England, and may be found on eel- 

 grass between tide-marks. 



According to A. Meyer, the end of the stalk when cut off 

 produced a new disk, and even pieces cut off between them 

 became complete Lucernarica, evincing the extraordinary 

 powers of reproduction in these interesting jelly-fish. 



Coming now to the true Discophora, jelly-fish, sea- 



