806 Proceedings of the Royal Physical Society. 



The following Communications were then read : — 



I. On the Anatomy of Sacculina with a description of the Species. By 

 John Anderson, M.D. Plate XIII. 



Three years ago I drew the attention of this Society to 

 the fact of the frequent occurrence of Sacculina and Pelto- 

 gaster on some of the Crustacea of the Firth of Forth. For 

 some years past the subject of the affinities of these parasites 

 has been occupying the minds of many foreign observers ; 

 and the following observations, therefore, are brought before 

 the Society in the hope that they may tend to throw some 

 light upon this difficult question. In the present paper I 

 have purposely abstained, as far as possible, from dogmatis- 

 ing regarding their systematic position, but elsewhere I have 

 referred them to the Cirripedes.* I may mention that the 

 relative position of the investing sacs, the character of the 

 ovaries and the ovigerous lamellae, and the apparent herma- 

 phrodite nature of the adult animal, when viewed in con- 

 nection with the larval form, appear to me clearly to indicate 

 their Cirripedial nature. Accordingly, in my graduation 

 thesis, I created a new order (Sacculinacea) for their re- 

 ception, t 



Among recent observers, Leuckart drew the attention of 

 naturalists to Thompson's systematic description of Saccu- 

 lina, and proposed the adoption of his generic term. " If 

 we restore," he says, " the name Sacculina either for Pelto- 

 gaster in Kathke's sense, or, at least, for the form character- 

 ised by Diesing as Pachybdella, we are only discharging an 

 old, superannuated debt." In the same article he described 

 a new form parasitic upon Hyas araneus, and which he 

 named Sacculina inflata. In accordance with Leuckart's 

 proposal, I use the term Sacculina as referring to the 

 parasite alluded to by Cavolini, and as synonymous with 



* Graduation thesis, "Contributions to Zoology." 



t The following are the characters of this order, as given in my thesis : — 

 Cirripedia sine segmentis, oculis et appendiculis. Carapax sacciforrnis et appen- 

 diculata est : foramen in carapace situin est. Pedunculus annulo corneo affixus 

 est. Os suctorium. Larva primo monocula cum 3 crurum paribus. Cir- 

 ripedia parasitica sub abdomine Crustaceorum Decapodorum Brachyurorum. 



