Respiratory Current in the Decapods. 21 



in the ^feffalopa-lsLVva, and in the course of growth this 

 number diminishes progressively until it sinks to one. 



The duration of the inversions is often very brief — about 

 the hundredth part of a minute ; but in a certain number of 

 species, such as Garcinus mcenas, it may be much greater 

 than this. I have established in the case of each species the 

 following number — to wit, the duration of the inverse circula- 

 tion in the space of ten minutes — counted in hundredths of a 

 minute *, and the results of my investigations are summarized 

 in the appended table (p. 22). 



In consequence of Prof. Giard having pointed out to me 

 the importance of the phenomenon of reversal for the compre- 

 hension of the ethology of the parasitic forms, I was led to 

 establish the following curious parallelism. 



We know that the crustacean branchial parasites of 

 Decapods are the Entoniscida3, Cepon, Bopyrus (sensli stricto), 

 and a few Copepods. 



Entoniscidge, the ethology of which has been so admirably 

 elucidated by MM. Giard and Bonnier, have frequently been 

 met with upon a Porcellana found upon the shores of Brazil, 

 in Garcinus mcenas, and in Portumnus latipes, Penn., which 

 lies buried in the sandbanks on the shore at Wiraereux. 

 Now Garcinus mcenas and Porcellana longicornis (which also 

 has its Entoniscid) are the only species — species not related 

 moreover — in which 1 have found for the inverse circulation 

 a number most nearly approaching 500 (that is to say, 5 

 minutes in 10). Po7'tumnus latipes is nearly allied to Por- 

 tumnus nasutus, in which the reversal, as described by 

 Mr. Garstang, is so strongly accentuated. In Portunus, 

 P. arcuatus is apparently the only species able to exhibit 

 periods of reversal of fairly long duration. Now this species 

 is infested with Entoniscidte much more frequently than 

 P. ruber and P. holsatus. Among the Oxyrhyncha, Achceus — 

 a genus allied to Stenorhynchus — is the only one that has 

 been found to support an Entoniscid. In Pilumnus hirtellus 

 these parasites are equally rare. Thus, except the latter, all 

 the hosts mentioned f belong to the third category of the 

 table. 



Cepon, as M. Giard caused me to observe, is not met with 



* This number, wliicli is necessarily approximate, corresponds to the 

 issue of carmine from the region of the latero-posterior inspiratory cleft 

 of the carapace, which is the easiest to observe — that is to say, the one 

 which is situated in front of the first thoracic limb. I have taken the 

 hundredth of a minute, since it frequently corresponds to a beat of the 

 scaphognathite, which I am therefore able to use as a metronome. 



t I have passed over Xardho and the Grapsidae, which I have not yet 

 studied. 



