SEMAEOSTOMEiE — CYANEA. 599 



the medusa. There is no ring-canal. The gonads are great hollow bags forming part of the 

 gastric system of the animal. There are deep clefts in the ahoral floor of the stomach giving 

 it a reticulate appearance (see fig. 3, plate 65). 



The gelatinous substance of the bell is translucent with a slightly bluish or yellowish tinge. 

 The entoderm of the gastrovascular system is of a rich brownish-purple and the mouth-arms 

 and oral curtains are chocolate-purple. The gonads and tentacles are either yellowish or 

 reddish-brown, and the muscular system of the subumbrella is brown or yellow. 



This species extends from the southern coast of New England northward to the Arctic 

 Ocean. It thrives best in the colder waters, and specimens found south of Cape Cod are 

 usually of small size. It is worthy of notice, also, that south of Cape Cod the medusae dis- 

 appear about the middle of June, while in the cold waters of the coast of Maine the mature 

 ones are most abundant in August and September. In Europe it is abundant off the coasts 

 from France to Northern Russia, and is found at Spitzbergen in August. 



Cyanea arctica appears to be identical with the so-called C. jerruginea of the North Pacific; 

 and C. postelsii of the Pacific is a closely allied form. 



The embryonic and larval stages have been studied by L. Agassiz, 1862; Fewkes, 1881; 

 Hamann, 1890; MacMurnch, 1891; and Ida Hyde, 1894. Agassiz gives a series of figures 

 illustrating the general developmental stages of the planula and scyphostoma, while Hyde 

 gives a very complete account of the histology of the early stages. The eggs are orange-colored 

 and provided with a membrane, and are dehisced from the ovaries into the gastric cavity, 

 where they undergo segmentation among the folds of the mouth-arms and finally escape 

 through the mouth of the parent medusa as free-swimming planulae. The segmentation is 

 total but unequal, the cells at one pole being smaller than those at the opposite pole. A 

 blastula is formed in which there is a large central blastocoel. The gastrula results from the 

 rapid divisions of one or two small cells at the small-cell pole, which form a layer that 

 invaginates. Hyde finds no wandering inward of free cells, but McMurrich records this 

 condition. The blastopore then closes over and the entoderm becomes entirely enveloped by 

 the ectoderm. In this condition the larva becomes a pear-shaped, ciliated planula and 

 swims actively through the water, the posterior, narrow end being that at which the gastrula 

 mouth had developed. One sometmies observes nematocysts in both ectoderm and entoderm 

 at this narrow hinder end of the planula. The next stage in development is instituted by the 

 formation of a shallow, crater-like, glandular invacination of the ectoderm at the broad, 

 anterior pole of the pear-shaped planula, and then the animal sinks down and attaches itself 

 to the bottom by this forward end. A cup-like depression of ectoderm then presses down 

 upon the entodermal sac at the narrow posterior end and finally fuses with it, and eventually 

 the mouth breaks through at this point. 



The first pair of the radial pouches is formed from the entoderm, the second, in part at 

 least, from the ectoderm of the crater. MacMurrich, 1891, and Hargitt, 1902, observed that 

 planulae in confinement encysted themselves during this stage, remaining thus for several 

 days until the mouth is about to break through, when the embryos emerge from the cyst 

 through a circular aperture at the center of its free, convex surface. Hyde, 1894, observed 

 this, however, only in one embryo and it is possibly an abnormal condition due to unfavorable 

 surroundings. Simultaneous with the formation oi the mouth 4 tentacles make their appear- 

 ance, and the scyphostoma finally acquires 15 to 20 tentacles. Hargitt, 1902, finds that lateral 

 stolons are sometimes produced by the scyphostoma, and secondary scyphostomae bud out 

 from these stolons. A number of ephyrae result from strobilization of the scyphostoma, and 

 this may occur in 18 to 20 days alter the planula has attached itself but this period varies 

 considerably. 



The young ephyra 3.5 mm. in diameter (plate 65, fig. 4) has a simple 4-cornered mouth 

 at the center of the subumbrella, and 4 smooth-edged, slightly raised lips. The 8 tentacular 

 notches in the margin are much wider and deeper than the notches of the sense-organs. The 

 tentacles arise from the bell-margin, but as the animal grows the margin extends be\ond 

 them and they thus come to project from the subumbrella floor of the disk. 4 short, ento- 

 dermal gastric cirri {gt plate 67, figs. 2, 3) are found upon the oral floor of the subumbrella 

 near the interradial corners of the mouth and project into the stomach-cavity. The gastric 

 system in this stage consists of a wide, lenticular, central stomach from which there extend 

 outward 16 simple, radiating pouches in the radii of the tentacles and sense-organs. In 



