22 Papers from the Department of Marine Biology. 
the first brood of larve. Hafele concluded that this was so.* But, 
as I have mentioned above, this question was answered in the opposite 
sense by observation of the moulting of an infected host. On Septem- 
ber 30 an Alpheid was collected which bore large external sacs, contain- 
ing Cypris larve, nearly all situated on the abdominal appendages. 
It was isolated and the next day was found to have moulted, the exter- 
nal sacs of course being carried away with the cast skin, which was 
preserved. Three days after this the host was examined to see whether 
any recurrence of external parasitic structures could be noted. A 
Fig. 12.—First abdominal appendage (right hand side) of Synalpheus brucei 
bearing external sacs of Thompsonia. X28. 
A. Cast skin showing external sacs (e. s.) containing nearly mature larve. Only 
two sacs are still present, the others having been accidentally detached, but 
the round black rings (ped.) indicate their position. 
B. The same appendage 3 days after moulting, showing the new crop of external sacs. 
number of pink bodies much smaller than any observed hitherto, but 
with the characteristic structure of the external sac, were found on the 
abdominal appendages. One of these was cut off and, after being 
examined alive, was fixed carefully. I give here two figures comparing 
the old external sacs on the cast skin and the new on the appendage 
after moulting (text-figure 12); they show that the distribution is 
roughly similar, but in no case are the positions identical. The new 
* Diese Reduktion der Organe hingt offenbardamit zusammen, dass die Parasiten nur 
einmal fahig sind, Nachkémmen zu produzieren, wie aus den Verhalten des Ovariums und Hodens 
geschlossen werden kann.”’ 
