22 



Papers from the Department of Marine Biology. 



the first brood of larvae. 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 larvae, 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 



e.s 



B 



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 larvae. 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 hangt offenbardamit zusammen, dass die Parasiten nur 

 einmal fahig sind, Nachkommen zu produzieren, wie aus den Verhalten des Ovariums und Hodens 

 geschlossen werden kann." 



