180 Dr. C. Claus on the Ephyre of 
striction of the vascular canal and the dorsal dilatation above 
the otolith-sac seem worthy of notice. 
With advancing growth the velar lobes, which are at first 
small and narrow, gradually increase in dimensions, while at 
the same time the periphery of the intermediate areas grows 
out at the expense of the lobes, which are transferred to the sub- 
stance of the disk, and the velar lobules seem to advance more 
and more into the zone of the alternating ocular lobes. Under 
these changes the larva gradually loses the character of the 
Ephyra in favour of the young Acalephan form distinguished 
by a circlet of marginal lobes. 
The sixteen areas of the vascular lamella become at the 
same time divided by vascular processes, which unite with 
each other into a great number of islets. First of all there is 
produced regularly between the radial canal and intermediate 
vessel a narrow pararadial vessel parallel to the latter, so that 
now thirty-two elongate ovate areas are present. ‘These are 
then somewhat irregularly interrupted by transverse vascular 
diverticula, and even in larve 4 millim. in diameter the 
rapidly advancing development of irregular radial series of 
areas is commenced, ‘The filaments are now already increased 
into small coil-like groups; and the buccal arms, by the en- 
largement of their processes, which are already contiguous, 
and by new formation of tentacles on their divergent terminal 
halves, have acquired a form in which the foundation of the 
pairs of arms unmistakably appears. Now also the comph- 
cation of the vascular network makes rapid progress. Larvee 
of 44-5 millim. diameter, already furnished with four pairs of 
arms cleft at the extremity, represent the stage which I lately 
described and figured as the youngest Cotylorhiza-larva 
known to me*, ‘The annular vessel, which was well marked 
at an earlier age, already appears indistinct and effaced to such 
a degree, that without a knowledge of the younger larva one 
might regard it as altcgether suppressed, and come to the con- 
clusion that the narrow-meshed vascular net of Cotylorhiza 
has a mode of formation quite different from that applying 
to Rhizostoma and the Aureliide. In larve of 7 millim. dia- 
meter, the areolation of the entodermal lamina already appears 
so narrow and close, and the frequently notched margin of the 
vascular network so far advanced peripheraily, that the generic 
and family characters are recognizable. ‘The further meta- 
morphosis of the larva in connexion with the general form of 
the disk, the marginal lobes, and the structure of the brachial 
* C. Claus, l. c. p. 52, figs. 106, 107. ‘The average size is here, by an 
oversight, stated as too small; it amounts not to 3 millim, but to 
5 millim, 
