SCYPHOMEDUSAE 



383 



The GASTRO- VASCULAR SYSTEM of Atollo chimi (Figs. 8 «, Z>) agrees on the whole with 

 the descriptions given by Vanhoeffen (1903) for A. valdiviae, by Maas (1903, 1904) for 

 bairdi and by Bigelow (1909) for ivyvillei, but there are differences enough to dis- 

 tinguish A. chiini from other species of the genus, even with the naked eye. The 

 rhopalar canals and tentacular pockets 

 are here strongly pigmented. The 

 rhopalar canals are thickened locally 

 in their outermost part and become 

 thinner again in the neighbourhood of 

 the rhopalium. Besides this a large 

 subumbrellar papilla lies in the middle 

 above each rhopalar canal. In young 

 specimens (Fig. 8 a) this is shaped like 

 a ball or egg, and in older ones (Fig. 8 b) 

 distally elongated to form a rounded 

 longitudinal ridge, which diminishes 

 in height towards the margin. Beneath 

 this papilla the otherwise dark rhopalar 

 canals are very poor in pigment and 

 become nearly transparent, so that they 

 are visible only by their outlines. The 

 sudden thickeningof the rhopalar canals, 

 combined with the bright transparent 

 oval spot formed by the papilla and 

 the dark purple-brown pigmentation 

 around it, gives its own cachet to the 

 gastro-vascular system of A . chuni. 



In the tentacular pockets the false 

 SEPTA, as already observed by Maas in 

 A. bairdi and by Bigelow in zvyvillei, 

 can almost always be observed. They 

 are very variable in form and size, 

 being long, short, broad, or narrow. 

 There is such great variability of these 

 septal regions subdividingthe tentacular 

 canals that they do not prove to be of any 

 systematic value as believed by Maas. 



The small and narrow vessels in the lappet pouches reach very far into the lappets 

 so that at their distal ends only a small piece of the endoderm lamella is still visible. For 

 comparison I give here two figures of the gastro-vascular system, the first showing that 

 of a young specimen of about 15 mm. diameter (Fig. 8 a) and the second (Fig. 8 b) that of 



Fig. 8. Atolla chiini, Vanhoeffen. Sector of the 

 gastro-vascular system. Ring muscle (on the 

 left) partly cut off. 



a, of a young specimen, about 15 mm. in diameter. 



b, of an adult specimen, about 50 mm. in diameter. 



