42 



Embryonic developrnent and Larvai Stages. 



and 18). In our figure the chitinous investment of the embryonic cells (eh fig. 20), which 

 will become the coat of the Kentrogon is clearly shown. 



The Cypris larva spencls a free and active existence for four clays, and it is then ready 

 to fix itself on the host. 



Delage who has observed the fixation of the Cypris larva on Carcinns maenas on nume- 

 rous occasions, states that fixation occurs at any point on the surface of the body or the 

 appendages, except on the under surface of the abdomen where the adult Sacculina is evagi- 

 nateci. The Cypris fixes itself by the hook on its antenna to a hair of the crab. I have 

 found Cypris larvae on two occasions upou the dorsal surface of the carapace of Inachus scorpio. 

 It cannot be disputed therefore that the Cypris larva may fix itself at almost any point 

 of the body of its host; ancl after fixation it undergoes a series of changes which evidently 

 have for their object the insertion of part of the cellular contents of the Cypris into the host. 



These changes, as described by 

 Delage, are shortly as follows: The 

 thoracic appendages and abdomen are 

 amputated and cast off, ancl a chitinous 

 investment is formed round the mass 

 of embryonic cells. The shell of the 

 Cypris is thrown away, and the Ken- 

 trogon larva is left affixed to the base 

 of the crab's hair. The base of the 

 hair is penetrateci by a chitinous tube 

 of the Kentrogon larva which pushes in- 

 to the sheath of the antenna, and the 

 "embryonic cells" pass through this 

 tube into the body of the crab. 



These processes are illustrateci 

 in the Text figs. 10 ancl il. 



It appears to me that two ques- 

 tions present themselves with relation 

 to the history of the fixation of the Cypris in Saceulina as described by Delage; firstly is 

 this method of fixation the normal method by which the Sacculina gains an entrance into 

 the body of the crab, and secondly of Avhat nature are the cells which enter into the 

 crab's body? 



It appears to me that the definitive answer to these questions can only be given by 

 studying the Sacculina soon after its entrance into the crab's body. This will be done in the 

 next chapter, and we shall find that with regard to the first question, the youngest internai 

 Sacculinae found must have entered the crab at some point other than the position of evagi- 

 nation of the adult body, in other words, most probably in the manner described by Delage ; 



K. 



Text figs. IO and 11. e = carapace of Cypris. Eni = embryonic cells. 

 k = kentrogon. eh = chitinous surface of crab. 1/ = hair. 



