JELLY-FISHES. JOl 



The sexual bells are of two kinds, male and female, and both are found m grape- 

 like clusters, the male near the base of the tasters and the female near the polypites. 

 If we isolate one of the members of a cluster, we find that it has a bell-like shape, and 

 that the ova or spermatozoa are found on a proboscis within. Each bell hangs from 

 the cluster by a tender peduncle which arises at its apex, and each female bell contains 

 a single ovum. 



The growth of the young Agalma from the egg to the adult is of a rather compli- 

 cated nature. When cast in the water the egg is a tiny, transparent sphere barely 

 visible to the naked eye. After fecundation, and obscure changes similar to a seg- 

 mentation of the yolk, a slight protuberance arises at one pole. This prominence is 

 formed of two layers between which, in a short time, a third layer is also formed. 

 The outer layer is the ectoderm, the middle the mesoderm, and the internal the endo- 

 derm. Between the endoderm and the remainder of the egg there is a cavity called 

 the primitive cavity. As the embryo grows older the elevation at one pole increases 

 in size, and the proportion in thickness of the middle layer, as compared with the 

 ectoderm and endoderm, becomes very large, while the ectoderm becomes very 

 thin. The prominence has now assumed a helmet-like shape, and fits like a cap 

 over the remnant of the yolk. The whole larva in this stage of growth is called the 

 primitive larva or Xiszio-stage, and the cap-shaped covering, the primitive scale. 

 The primitive scale is an embryonic organ which is lost in subsequent development 

 of the larva. 



Immediately after the primitive larva stage there is found to develop under the 

 primitive scale an air-bladder or float, which first appears as a little bud near the open- 

 ing into the primitive cavity, which has now taken the form of a tube in the primitive 

 scale lined with endoderm. At about the same time also there appears a covering- 

 scale of very different form from either the cap-like .primitive scale or the covering- 

 scale of the adult Agalma, which have already been described. The float is the 

 permanent float of the adult, while the second formed covering-scale, like that of the 

 first, is also embryonic and larval in character. The larva has now the followino- 

 parts: 1, The remnant of the yolk; 2, a cap-shaped covering-scale; 3, a second em- 

 bryonic covering-scale, and 4, a float. As the larva grows older more covering- 

 scales like the second appear, and the beginnings of a tentacle and tentacular knobs 

 are seen at the adjacent end of the growing larva. At the same time the yolk 

 becomes elongated, and in its walls appear reticulated masses of red or crimson 

 pigment. 



The tentacle first formed as well as its pendants, the embryonic tentacular knobs, 

 are transient in character. They differ essentially from the adult knobs, and are 

 confined to this stage in the development of the larva. Meanwhile the primitive scale 

 is lost, and a circle of covering-scales of the second kind appears at the base of the 

 float. This larva is called the Athorybia larva from its i-emote resemblance to a related 

 adult genus called AtJwrybia. The appendages of this larva are : 1, a float; 2, a crown 

 of embryonic covering-scales; 3, the remainder of the yolk-sac with an attached 

 tentacle and temporary pendants. 



The next following larval condition of Agalma is one in which the embryonic 

 covering-scales have disappeared and new scales like those of the adult have formed. 

 Pour well-developed nectocalices appear on a nectostem, and an adult polypite bearing 

 the characteristic pendants of the adult has grown on the extremity of the short polyp- 

 stem. A remnant of the yolk-sac, however, still persists, and from it depends an embry- 



