MEDUS.^. I. 



15 



Table I. Synoptic Table of the Species of Chromatonema. 



Diameter of full-grown medusa 



Number of tentacles in full-grown medusa 



Number of cordjli between each successive pair of tentacles 



Occurrence ' 



C. rubrum 

 I'ewkes 



24 —27 mm 

 ca. 24 

 2 (I) 

 Northern At- 

 lantic Ocean 



C erythrogonon 

 Bigelow 



C. hertwigi 



Vanhoffen 



38 mm 



ca. 64 



I (2J 



Eastern tropical 



Pacific 



50 mm 

 20 

 5 



Indian Ocean 



Systematical Position. — The structure of Cliroiuatojicnia presents, in several regards, a 

 considerable resemblance to the members of the family Laodiccidcr previously known, particularly to 

 the genera Laodicra and Plychogoia. In all of the three genera the manubrium has the same shape: 

 the square stomach, the broad base of which is attached to the subumbrella along the arms of a 

 perradial cross; the short, wide month-tube, and the folded mouth-edge, in the four corners of which 

 lips are just indicated. Common for the three genera is, moreover, the structure of the four radial 

 canals; the proximal part of each of the canals contains the gonads; the ventral part of this gonadial 

 , part is funnel-shaped and is the proper digestive part of the canal. In Chromatonema as in Ptyclwgnia 

 the dorsal line of attachment of the radial canal to the subumbrella is pinnate, and in older individu- 

 als of all of the three genera the proximal part of the gonads may be developed within the corners 

 of the stomach in the dorsal wall of the latter on both sides of the arms of the perradial cross. But 

 with regard to the structure of the gonads Cliromatonciua presents a considerable difference, not only 

 from Ptychogena and Laodicea^ but from all other Leptomedusae. As described above each of the radial 

 canals in C/iromafoiirma carries two rows of sack-.shaped gonads, completely independent of one another. 

 In all otlier Leptomedusae each radial canal bears either two lateral gonads, forming two continuous 

 masses in the ectoderm of a certain part of the lateral walls of the canal, or only one gonad com- 

 pletely surrounding a shorter or longer part of the canal. (A special case is the gonads of certain 

 species of Eutima, being trans versally divided into two separated pairs 

 of gonads, one pair on the subumbrella, one pair on the stomachal peduncle). 

 In some forms the gonadial bands are straight and linear, in others they 

 are more or less undulated or folded. In Laodicea the lateral walls of the 

 gonadial parts of the radial canals have a number of short lateral pouches; y 

 in Ptychogena these pouches are mucli more highly developed and have 

 attained the shape of vertical lamellae, the dorsal edges of which are atta- 

 ched to the subumbrella; but still there is only one gonad on each side of 

 the canal; there is only one gonadial band, but it is highly folded. In 

 Staiirophora the gonads have a similar structure, but the folding is still 

 more complicated. 



The structure of the gonads of a Cliyomato>icma and a Ptychogena 

 may be illustrated by a diagrammatic figure as the textfig. 4. This diagram corresponds to that by 

 which Hartlaub (1914, p. 347) illustrates the typical folding of the gonads in the two groups of 

 TiaridcE, viz. the Calycopsidcr and the Neotitrridcr. It is not difficult to refer the two types to a common 



Fig 4. Diagrams, showing the 

 structure of the gonads of 

 Chromatonema (a) and Ptycho- 

 gena {b). — / inner side, o outer 

 side. 



