28 



FOSSIL MEDUSA. 



1-3 of PI. I), but in the great majority it could only have been very narrow 

 and deep. Whether it was more than a simple tube, uniting the radial 

 exumbrella canals and the oral canals, is doubtful. In such specimens as 

 those represented by figs. 4, 4 a, 4b, 8, 8 a of PI. I, there is little space for 

 any central divisions of the intestinal canal. Such a space is represented, 

 however, in text figs. 6 and 7, as it is improbable that a simple intestinal 

 canal existed in such forms and the divided canal in others, like text fig. 4. 

 In the fossils the central axis or disk is usually distorted by compres- 

 sion and penetrated through and through by fine annelid borings. The 



presence of the central stomach is sug- 

 gested by the frequent collapse of the 

 central disk immediately above its nor- 

 mal place (PI. I, fig. 2); over forty 

 individuals before me show this with 

 marked distinctness. The central 

 stomach is clearly indicated in fig. 4 of 

 PI. Ill, where the radial intestine of the 

 exumbrella lobes passes into it. This 

 is also shown in the transverse sections 

 (PI. IV, figs. 7, 8, 9) and in vertical 

 sections (PI. IV, figs. 10, 11). The 

 buccal stomach is indicated by fig. 8b 

 of PL II. 



coronal intestine. — By this term Haeckel 



includes the entire peripheral gastro- 

 vascular system of medusas which sur- 

 rounds the central or principal intestine and communicates with it by the 

 gastral opening. He considers that in the Acraspeda the typical and origi- 

 nal arrangement was four wide perradial pouches, which begin at the cir- 

 cumference of the central stomach and run in the subumbrella toward the 

 umbrella margin, where they are united by a coronal canal. 



This typical quadripartite pouch corona of the Scyphomedusa; has been developed 

 from the simple gastral space of their aucestors, the Scyphopolyps, by the four inter- 

 radial taniiola of the latter being laid together and fused at four points (of equal 

 height), or in four streaks, by their upper dorsal parts and lower ventral parts. In 

 this way four small iuterradial nodes or narrow ridges are originated, which form 

 incomplete septa between four wide perradial pouches. 1 



Fig. 4. — Brooksella alternata. Diagrammatic central 

 vertical section through the umbrella lobes. 



a, exumbrella lobes, with radial canals; d, section of 

 umbrella lobes; o, oral arms, with interior canal; /, 

 undifferentiated central axis that in the living animal 

 was probably the seat of the genitalia, etc., as in some 

 recent forms (see text fig. 3, p. 11); g, position of the 

 central stomach; h, position of the buccal stomach; i, 

 points extending downward in the stomach that suggest 

 a former opening to a central mouth; Jfc, axial canals, 

 corresponding to the pillar canals of text fig. 3, p. 11. 



■Haeckel, loc. cit., p. lxxxix, par. 12G. 



