Miscellaneous. 535 



On Entoniscus mteaadis. By M. A. Giard. 



Almost at the moment when I made known the existence on the 

 French coasts of the Entoniscus parasitic upon Fachi/i/rapstts mar- 

 monitus, Fab.*, P. Fraisse met with this curious Isopod in the Bay 

 of Naples, that is to say in the locality whei'e it was discovered in 

 1787 by Cavolini. Fraisse further stated t that he had found the 

 same parasite in Carcinus mfenas, but he did not establish the cor- 

 rectness of this determination by the comparative examination of 

 the embryos, which furnish the best specific characters in creatures 

 which are so profoundly modified in the adult state. As I had 

 observed at various points on the shores of the Channel embryos of 

 Entoniscus which had strayed into the incnbatory cavity of Sacculina 

 Carcinl, I repeatedly sought for Entoniscus in Carcinus mcenas, 

 but always without success, notwithstanding the great number of 

 crabs which were sacrificed for this purpose. 



I have been more fortunate this spring, and the first crab which 

 I opened at Wimereux furnished me with a fine Entoniscus, the 

 ovigerous lamellae of which contained perfectly mature embryos. 

 The infested Carcinus mcenas was a female of middle size, bearing a 

 Sacculina the incubatory cavity of which was empty. The Ento- 

 niscus was placed on the left side of the crab, in the midst of the 

 hepatic caeca of its host. 



This Entoniscus, which I shall call Entoniscus mcenadis, is very 

 distinct from Entoniscus Cavolinii. The liquid which circulates in 

 the vessels contrasts by its red colour with the orange-yellow ground 

 of the ovarian mass. The ovigerous sac, or, to be more exact, the 

 mass of embryos ready for exclusion, presents a mauve-grey colora- 

 tion, very different from the leaden tint of Entoniscus Cavolinii 

 loaded with ova in the same stage of development. The embryo, 

 especiallj-, presents easily recognizable differential characters.^ We 

 find no trace of the remarkable ll^auplian eye, the existence of which 

 I have indicated in the parasite of the Grapsus. The crystallines of 

 the lateral eyes are more approximated, and from these eyes there 

 start, on each side of the head, arcs of a reddish-brown pigment 

 which meet upon the median part of the forehead. The sixth 

 pair of thoracic legs presents nearly the same conformation as the 

 corresponding pair in the embryo of E. Cavolinii ; nevertheless the 

 terminal rod is shorter, and does not support a tuft of hairs as in 

 the latter. From this point of view E. Cavolinii and E. mcenadis 

 diff'er greatly from E, Salvatoris, Kossmann, in which the six pairs 

 of thoracic feet are all similar J. 



Kossmann has placed beyond doubt the existence* of the male in 

 the European Entonisci§. Farther, he has supposed that in the 



* ' Comptes Rendus,' August 12, 1878. 



t Arbeitena. d. zool.-zoot. Inst, zu Wiirzburg, Bd. iv. 1878. 



I I resume, for the parasite of Portumis arcuatus, the name originally 

 given by Kossmann, because this parasite appears to me to be specifically 

 distinct from that of Portunus puber, E. Moniezii, with which Kossmann 

 would identify it. 



§ See Kossniauu's paper translated in the Ann. & Mag. Nat. Hist. 

 ser. o, vol. x. p. 81. 



