464 MEDUSA OF THE WORLD. 



The researches of McCrady, 1857, Brooks, 1886, and H.V. Wilson, 1887, have shown that 

 during development the larva produces other larvae like itself by budding. The life-history 

 is as follows: The segmentation stages and early development of the ovum are unknown. 

 The larva becomes an elongate, 2-layered, ciliated planula, in which condition it swims freely 

 through the water and finally attaches itself by its mouth to the bell-margin of Turritopsis 

 nutricula McCrady. The cilia then disappear and 2 tentacles develop at the aboral pole of 

 the planula, and these are soon followed by 2 more tentacles situated 90 from the first pair. 

 At about this time the larva enters the bell-cavity of its host and clings to the wall of the 

 subumbrella by means of its tentacles, and while in this position it acquires a long cone-shaped 

 throat-tube that enables it to insert its mouth into the mouth of the Turritopsis, and in this 

 condition it leads a parasitic life. The larva is now in the "actinula " stage, for its appearance 

 recalls the actinula larva of Tubularian hydroids but in Narcomedusae the actinula may 

 develop directly into a medusa and not into a hydroid-stock. In other species, however, it 

 produces medusae only by budding. 



While the young Cunoctantha octonaria is in the actinula stage, other similar larvae are 

 often budded off from its aboral pole between the tentacles. These develop exactly as did the 

 original larva and finally become free medusae. 



The umbrella first appears as 4 lobe-like outgrowths between the bases of the 4 tentacles. 

 These lobes contain prolongations of the gastric cavity. The 4 tentacles retain their primitive 

 position and thus come to lie in the notches between the lobes. The 4 primary lobes become 

 8 by the stoppage of growth of both ectoderm and entoderm at the middle point of the periphery 

 of each lobe. As yet there are but 4 tentacles. 4 other tentacles soon appear, however, and 

 then the umbrella consists of 8 lobes with a tentacle arising from each notch between the lobes. 

 Later the velum grows between the lobes forming an interlobular web. The gelatinous sub- 

 stance of the exumbrella increases greatly in volume and grows over the bases of the tentacles, 

 and thus the tentacle-roots become imbedded. When the young medusa is about 1.25 mm. 

 in diameter, it leaves its host and leads a free existence (plate 55, fig. 2). At this time it has 8 

 tentacles and 8 marginal sense-clubs and is much like the adult in general appearance, except 

 that the peripheral outline of the gastric cavity is a circle running through the intersection 

 points of the 8 tentacles. At a much later stage an entodermal fusion takes place in the 

 interradii and thus the 8 radial pouches of the stomach are formed. 



Good accounts of the life-history of this medusa have been presented by McCrady, 1857, 

 and by Brooks, 1886, and an excellent description of its finer structure has been given by H. 

 V. Wilson, 1887. 



The medusa is apparently found in all tropical oceans, for Maas describes it from the 

 Malay Archipelago, and Bigelow from the Pacific coast of Mexico. It is common at Charles- 

 ton, South Carolina, and Beaufort, North Carolina, where it infests the bell-cavities of Turri- 

 topsis nutricula. It has not been found either at Newport, Rhode Island, or at Tortugas, 

 Florida, although T. nutricula is common at both of these places. It is a shallow-water species 

 and is often seen in harbors. 



Cunoctantha octonaria var. kbllikeri. 



Plate 54, figs. 4 to 9. 



Cunirta kbllikeri, MUller, 1861, Archiv. fur Naturgesch., Jahrg. 27, p. 41, taf. 4. 



(?) Cunoctantha octonaria, Maas, 1905, Craspedoten Medusen der Siboga Expcd., Monog. 10, p. 67, taf. 12, fign. 77, 78; taf. 13, 

 fign. 83-85; 1906, Revue Suisse de Zoo]., tome 14, p. 98, plate 3, fig. 11. 



Cunoctantha kollikeri Miiller, 1861, from the coast of Brazil, bears a close resemblance to 

 C. octonaria, and the same medusa has apparently been described by Maas, 1905, from the 

 Malay Archipelago. Maas, however, describes a hood-like, or scale-like, expansion of exum- 

 brella ectoderm over each marginal sense-club, and such expansions have not been seen in C. 

 octonaria. 



In both Miiller's and Maas's medusae the remarkable feature is the presence of numerous 

 Cunina larvcE within the stomach-cavity of the medusa. There are often 60 to 80 ot these 

 larvae developing within a single mother-medusa. In their early stages they consist of 7 to 12 

 outer cells which form a single layer inclosing 2 to 3 inner cells. These inner cells are all ot 



