456 Mr Potts, Thompsonia, a little known Crustacean Parasite. 
have been lost. The mantle is a thin layer of tissue, also without | 
muscles, existing to secrete the outer envelope of chitin. The 
mantle cavity has virtually disappeared, the inner surface of the | 
mantle being adherent to the visceral mass. Until the larvae 
are advanced in development no aperture is found in the mantle, 
and the envelope of chitin is entire. The visceral mass is occupied 
entirely by the ovary. In this the ova grow, mature, and undergo 
the whole of their development. Reproduction appears to be! 
parthenogenetic, for I have been unable to find any trace of 
a testis or of free spermatozoa. The description of a testis in- 
T. japonica by Hiifele seems to me of very doubtful value: no} 
spermatozoa were observed by him. The Nauplius stage is omitted’ 
from the life history, and the larvae reach the Cypris stage while’ 
still within the egg membranes. When development has reached) 
this point the ovary has completely disintegrated, and eventually) 
the larvae burst their membranes and lie freely within the mantle. | 
At the same time a definite aperture is formed in the mantle at) 
the apex of the sac and a moult of the external cuticle allows the 
larvae to escape. On this point my observations are in agreement' 
with those of Coutiere, and Hafele’s statement as to the absence) 
of an aperture is probably due to the fact that the individuals he! 
examined were not sufficiently mature to show this point. 
As the visceral mass thus disintegrates with the birth of 
a brood of larvae, the question arose whether the stage of 
reproductive maturity is terminated when a single brood has 
been produced. This was answered conclusively by observations 
made upon infected Synalpheus which had been kept in captivity! 
for some days. One or two individuals moulted, and it thus 
became evident that the effect on the host in this respect is more 
comparable to that of Peltogaster on the hermit crab than ol) 
Sacculina on the true crabs, where the moulting function is 
suppressed. In the case which was followed most carefully the 
external sacs were of large size and approaching maturity when 
moulting took place and they were carried away with the 
cast skin. Three days afterwards the appendages were examined 
to see whether any new external parasitic structures were 
visible. A number of pink sacs, much smaller than any observec 
hitherto, but with the characteristic structure of the external sac’ 
were found on the abdominal appendages. Clearly, then, successive 
crops of sacs containing the reproductive organs are produced bj 
the root system. It was mentioned above that the finer divisions 
of the roots observed in the appendages ended sometimes 11 
external sacs and sometimes in club-shaped enlargements whiek 
did not penetrate the cuticle. It is these structures which are 
destined to produce a new crop of external sacs. Already in man) 
' cases the typical organisation can be recognised. The periphera’ 
