Royal Physical Society. 451 



9. False medusoid (ovary with rudimentary umbrella) of Hippopodius 

 Neapolitanus (Kolliker). 

 10. False free medusoid of Diphijes (Huxley). 

 LI, 12, 13, 14. Development of false medusoid or marsupium in Sertularia fallax . 



Under the title of Laomedea dichotoma, Johnston has de- 

 scribed as varieties two very distinct zoophytes. One (the Sea- 

 thread Coralline, Ellis, Corall. 21, No. 18, Plate XII., fig. 

 a, A), a magnificent production, attains a height of twenty-four 

 inches, its slender stem and branches hidden by thousands of 

 snowy polyps, the whole forming a pyramidal mass, which 

 sways to and fro with every movement of the waves ; while 

 from the axillae of the branches the reproductive cells pour 

 forth shoals of flapping medusoids, which fill the water around 

 with a cloud of living beings. Many of these beautiful trees 

 are joined together by anastomosing lines of creeping fibres, 

 which wander over the rocks, and unite them as a single living 

 being. The other variety {the Sea-thread Coralline of Ellis, 

 plate xxxviii.) is very different from the last. It is a shrubby 

 Zoophyte, of robust habit, the imperfect medusoids of which 

 remain fixed to the top of the reproductive cells, where they 

 serve as marsupial pouches for the development of the ova. 



The reproductive cells are developed from the axillse of the 

 branches, and are at first traversed by a fleshy column, which 

 occupies the axis of the cell, and, being dilated at its summit, 

 closes the orifice. This column differs in no respect from the 

 ordinary alimentary polyp at an early stage of development, 

 and must be considered as a polyp in which development has 

 been arrested, in order to render it subservient to the func- 

 tion of reproduction. 



In the female (Plate XXIII., fig. 3) we find a number of sacs 

 developed from the reproductive polyp, each of which consists 

 of, — 1st, An ovarian sac formed of two layers, a four-lobed 

 endodermal process or layer (a), and an ectodermal layer (6), 

 between which are contained one or more ova; and, 2dly, Of an 

 investing capsule, which becomes converted into the umbrella, 

 with lateral canals and tentacles of an imperfect medusoid (d), 

 of which the ovarian sac is the peduncle. After the medusoid 

 has issued from the top of the cell, the ova still remain in the 

 peduncle or ovarian sac, but the outer membrane or ectoderm 



