954 MB. A. T. WATSON ON THE STRUCTURE 
animal’s development these cells first appear. I have failed to 
detect them in the youngest specimens (only 10 mm. long), 
which were obtained by the kindness of Dr. Herdman from 
Naples; but I found them fairly well developed in other 
specimens (only 16 mm. long) which, though probably only a 
few weeks older, were full of ova. In order to reach these 
pores, the genital products pass through the sphincter septal 
valves (s.v., Pl. 23. fig. 5), which can easily be traced in the 
sections right up to the lumina of the pores. On one occasion, 
whilst examining a preserved Ammochares from Naples (which 
in 90 per cent. alcohol had uot become hardened), I accidentally 
caused these pores to open and work by osmotic action, the 
specimen having been transferred to spirit of a different strength. 
The ova, deposited on the 17th July 1898, were examined 
every 24 hours and sketched from life from the 19th to the 21st 
inclusive (Pl. 25. figs. 14-18). On the second day, the eggs 
were in the morula stage, and a few specimens, which had been 
transferred from the aquarium to a small glass dish, had, on the 
20th July, attained the two different forms represented by 
figs. 15 & 16, Pl. 25. 
In view of the subsequent development, it is interesting to 
note that, whilst watching the specimen fig. 16, I observed, now 
and then, a thread or two, with a cell at the extremity of each, 
shot forth from the point (m/), the threads being immediately 
retracted. Fig. 15 is also deserving of special attention, since it 
corresponds, most closely and suggestively, with a stage in the 
development of the Hydrozoa, as shown in Fewkes’ figure of 
Agalma (11. pl. ii. fig. 12) of somewhat similar age. It was 
found that development had been retarded by removal, as speci- 
mens taken the same evening from the aquarium had reached 
the stage with characteristic sete, fig. 17, which will be recog- 
nized as Mitraria. On the following evening, the specimens 
in the glass dish were found dead, and those in the aquarium, 
although vigorous, had apparently made little or no further 
progress in development. The larva attached itself by its sete 
to the bottom, and, using them as a pivot, rotated in a top-like 
fashion in the watch-glass, whilst four others, affixing themselves 
by the same means toa speck of floating organic matter, in the 
form of a cross, caused it to revolve like a miniature wheel. 
This rotation was doubtless due to cilia at the apex of the bell, 
as the motion of those at the margin was scarcely perceptible. 
