32 THE MEDUSAE. 



The gastric cirri present a somewhat different condition from that figured 

 by Maas (: 03, taf. 3, fig. 16). They are arranged in four groups, each 

 group arising from a single stout stalk (PI. 11, fig. 4). There are in all from 

 eighty to one hundred filaments. 



The peripheral canal system was easily demonstrated in one specimen by 

 injection with carmine. In general, as is shown in PI. 12, fig. ^ it 

 resembles the type of Periphylla, there being twelve broad radial canals, six 

 rhopalar and six tentacular, separated one from another by narrow septal 

 regions. At the bases of the marginal organs the canals divide, the branches 

 of adjacent canals uniting in the marginal lappet to form a festoon canal. 



The specimens are especially valuable for the light which they throw on 

 the structure of the gonads. These, four in number, are apparently double 

 structures (PI. 12, fig. £). Such a double appearance has already been noted 

 both by Vanhoffen (: 02") and Maas (: 03) ; but while Vanhoffen believes that 

 they are actually paired structures (: 02% p. 30), Maas doubts if this is the 

 case, though he could not determine whether the lighter zone in the middle 

 of each was the line of division between two of a pair of gonads, or was the 

 region where the genital products are released. To settle this point defi- 

 nitely I prepared a series of cross sections of one of the gonads of a male 

 individual, from which it was at once evident that the gonad (PI. 12, fig. 3) 

 is a single leaf-like structure, so folded as to leave a deep groove along its 

 middle line, on the inner surface. It is this groove, extending throughout 

 the entire length of the gonad, which forms an apparent line of separation. 

 Furthermore, there is but a single line of attachment for each gonad. The 

 gonads of a female individual are filled with a comparatively small number 

 of large eggs (PI. 11, figs. 1,2) so that the double appearance is not so evident. 

 The specimens are so perfect that there is no doubt that four is the normal 

 number of gonads, as Maas (:03) has stated, not six, as Vanhoffen (:02*) believed. 



The ring muscle is very weak, indeed hardly distinguishable as such, 

 much as in Periphyllopsis. Subumbral plates, such as have been described 

 for Nausithoe (Maas, : 03, p. 20) are, on the contrary, very prominent, par- 

 ticularly at the bases of the tentacles (PI. 11, fig. 3). 



The gonads are orange-yellow ; otherwise the specimens are entirely 

 colorless. 



A. vanhqfeni is no doubt a surface species, and it is possible that the 

 same is true of A. subglohosa, since both captures of the latter were made 

 with open nets. 



