M. Leuckart on the genus Sacculina. 423 



lie also remarks expressly that Peltogaster can hardly be placed 

 in the same group with the true suctorial worms and Trematoda, 

 which it approaches as regards its organ of adhesion. Notwith- 

 standing this, however, and although in the iuterim the simi- 

 larity of Peltogaster with " the parasitic females of some of the 

 lower Crustacea" had been pointed out by me*, we find our 

 animals placed amongst the Leech-like parasitic worms in the 

 f Systeina Helminthum' published by Diesing some years after- 

 wards (1850), and now indeed distributed into two genera, — the 

 species with a terminal sucking-disc found by Rathke under the 

 abdomen of Carcinus Mcenas being formed into the type of a 

 new genus, Pachybdella, Dies. (P. Rathkei, Dies., Peltogaster 

 Carcini, Rat like). 



That this attempt at a systematic arrangement is a mistake, 

 cannot be a matter of doubt to any one after the critical and 

 historical remarks of Steenstrup f. Steenstrup proves that the 

 animals in question were not only discovered by Kroyer J on 

 Pagurus and Hippolyte simultaneously with Rathke, but were 

 already described and figured unmistakeably by Cavolini § in 

 the last century. Cavolini also observed the young of our ani- 

 mals, which at certain times issued in abundance from the free 

 opening of the body regarded by Rathke as the mouth. He 

 even recognizes their unmistakeable similarity to the larval forms 

 of the Cyclops. But that the sacs from which these larvae pro- 

 ceeded were animals, and, indeed, the parents of the larvse, re- 

 mained unknown to the Italian observer ; he regarded them as 

 mere ovisacs which were in this case abnormally attached to a 

 strange animal (Pagurus). Both by Kroyer and Rathke the 

 animal nature of the sacs in question was certainly recognized ; 

 but their relations remained almost equally uncertain to the 

 Danish zoologists. In their opinion, these parasites form a 

 new genus with several species (Kroyer was acquainted with 

 three from Pagurus pubescens, P. Bernhardus, and Hippolyte 

 pjusiola), which, on the one hand, appears to have some analogy 

 with the Lerncea, but, on the other, possesses a certain affinity 

 also to the Hiruditiea and other Entozoa. 



Some years after Rathke and Kroyer, the same creatures, as 

 Steenstrup remarks, were also observed by Bell || on the abdo- 

 men of Carcinus Manas and Portunus marmoreus, from the 

 English Channel, and cursorily described by him. Bell appears 



* Morpbol. dei- wirbellosen Tbiere, 1848, p. 72, note 2. 



t "Wiegniann's Arcbiv, 1855, p. 15; translated in Ann. Nat. Hist. 2nd. 

 ser. vol. xvi. p. 153. 



\ Monogr. der nordiscben Hippolyte-Arten, in Vid. Selskab. Naturv. og 

 Math. Afh. ix. d. p. 56. 



§ Abb. iibev die Erzensnng der Fiscbe und Krebse, p. 161. taf. 2. 



|| Hist. Brit. Crust. 1845, p. 108. 



