lxxxii THE VOYAGE OF H.M.S. CHALLENGER. 



a more or less distinct cruciate form, as four perradial archings outwards alternate with 

 four interradial archings inwards in the same fashion as in the oral cross and the palatine 

 cross (PI. XXXII. figs. 3, 4). We therefore term the four perradial limbs of the central 

 gastral cross, the cruciate chambers, and the four interradial gelatinous pieces of the 

 umbrella, projecting centripetally between them, the cruciate columns. The latter 

 correspond morphologically to the interradial centre of the obelisk plates, and at the 

 same time to the central section of the taeniola. The cruciate form of the central stomach 

 is prominently developed in many Anthomedusae (System, taf. iv., figs. 7, 9), the 

 Leptomedusa (System, taf. viii. fig. 6), Stauromedusae (System, taf. xxi., xxii.), and 

 Discomedusae (System, taf. xxviii., xxix., &c). The cruciate chambers are most strongly 

 developed in the sub-order of the Rhizostomae, in which they are often considerably 

 larger than the central cruciate cavity (System, taf. xxxvii.-xl.). The cruciate chambers 

 attain special importance, when the reproductive glands are mostly or entirely developed 

 in them ; in such cases they are sometimes developed into independent genital pouches 

 as in many Anthomedusae and Discomedusae. 



§118. Gastral fissures (" ostia gastralia," go). The communication between the 

 central principal intestine and the peripheric coronal intestine in all Medusae takes 

 place exclusively by means of the radial " gastral fissures," which are usually limited to 

 the side-wall of the central stomach. The number of these gastral ostia corresponds to 

 that of the chambers of the coronal intestine which open into the central stomach, and 

 therefore amounts to four in the majority of the Medusa?. Four secondary interradial 

 gastral ostia are, however, often added to the four primary perradial, and sometimes also 

 a larger and usually variable number of succursal gastral fissures. The latter vary 

 extremely in form and size; In general, the gastral ostia naturally form large and wide 

 fissures in those Medusae, whose coronal intestine consists of broad pouches and narrow 

 septa, therefore in most Acraspedae, and, for example, in the Tesseroniae, the Cannostomae, 

 and in the Typhlocannae among the Semostomee (Pis. XV.-XXXL). On the other hand 

 the gastral ostia form small and narrow holes in those Medusas, whose coronal intestine 

 is composed of narrow canals with broad septa ; therefore in most Craspedotae, both in 

 the Cyclocannae and Rhizostomae, among the Discomedusae (Pis. I. -VIII. , XXXII. ). 

 According to their position, the gastral openings sometimes lie vertically, sometimes 

 obliquely, sometimes horizontally. Most Tesseroniae are distinguished by very large, 

 wide gastral ostia ; they lie vertically or subvertically in most Peromedusae, and in one 

 part of the Stauromedusae (Pis. XVI. -XXV.), whilst they are horizontal or sub-horizontal 

 in most Cubomedusae (PI. XXVL), and in another part of the Stauromedusae ; in all 

 cases the margins of the gastral ostia are entirely or for the most part edged with 

 phacelli (PI. XVII. fig. 21). Sometimes, namely in the Cubomedusae, there are valves 

 by which the gastral ostia can be closed. The small Narcomedusae group of the 

 Solmonetidae, in which the entire coronal intestine is obliterated, is distinguished by the 



