JELL Y-FISHES. j qj 



The sexual bells are of two kinds, male aud female, and both are found in grai>e- 

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

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

 that the ova or spermatozoa are found on a proboscis witliin. Each bell hano's from 

 the cluster by a tender peduncle wiiich arises at its apex, and each female bell cdntaius 

 a sin^'le ovum. 



The'urowth of the young Aijulma from the egg to the advdt 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 se"'- 

 mentation of the yolk, a slight protuberance arises at one jjole. 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- 

 dcrm. 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 

 ec'toderm 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 

 <)\er the remnant of the yolk. The whole larva in this stage of growth is called the 

 primitive larva or ii'«3«a-stage, and the cap-shaped covering, the primitive scale. 

 The primitive scale is an embryonic oig'au which is lost in subsecpient development 

 of the larva. 



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

 Ijrimitive scale an air-bladder or float, which first ajjjjears 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 apjiears a covering- 

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

 scale of the adult Aijalma, which have already been described. The float i.s 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 following 

 parts : 1, The remnant of the yolk ; 2, a cap-shajjed 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 tentaculai- knobs 

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

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

 pigment. 



The tentacle first formed as well as its pendants, the embryonic tentacidar 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 remote resemblance to a related 

 adult genus called Athorybia. 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 temjiorary pendants. 



The next following larval condition of Af/alma is one in which the endjryonic 

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

 Four well-developed nectocalices appear on a nectostem, and an adult polyinte 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- 



