Dr. J. Anderson on the Anatomy of Sacculina. 13 
of the Crustacea of the Firth of Forth. For some years past the 
subject of the affinitics 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 dogmatizing regarding their systematic position, but else- 
where 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 lamelle, and the apparent herma- 
phrodite nature of the adult animal, when viewed in connexion 
with the larval form, appear to me clearly to indicate their Cirri- 
pedial nature. Accordingly, in my graduation thesis, I created 
a new order (Sacculinacea) for their receptiont+. 
Among recent observers, Leuckart drew the attention of na- 
turalists to Thompson’s systematic description of Sacculina, and 
proposed the adoption of his generic term. “If we restore,” he 
says, “the name Sacculina either for Peltogaster in Rathke’s 
sense, or, at least, for the form characterized by Diesing as Pa- 
chybdella, 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 
Peltogaster carcint, Rathke, and Pachybdella Rathket, Diesing. 
The Larva. PF. I. fig. 1. 
The larva, in the first stage, is oval, and presents no marks of 
segmentation. Placed near the centre of the anterior margin of 
the body is a yellow speck—the eye (a). The ocellus is placed 
nearly in the centre of a dark-coloured ring (4). Krohn, who 
has observed a structure similar to this in the larva of a Bala- 
nide, regards it as the cesophageal ring. The lateral margins 
of the body, on either side of the ocellus, are prolonged into two 
horns (c); and in this respect the young resembles the Cirri- 
pedian larva in its first stage. It is provided with three pairs 
of natatory legs: the first pair (d) are situated immediately pos- 
terior to the horns of the carapace; they are uniramous, are 
provided at their extremities with bristles, and appear to be 
* Graduation thesis, ‘Contributions to Zoology.’ 
y ‘The following are the characters of this order, as given in my thesis :— 
Cirripedia sie segmentis, oculis ef appendiculis. Carapax sacciformis et 
appendiculata est: foramen in carapace situm est. Pedunculus annulo 
corneo affixus est. Os suctorium. Larva primo monocula eum 3 crurum 
paribus. Cirripedia parasitica sub abdomine Crustaceorum Decapodorum 
Brachyurorum, 
