Miscellaneous. 425 
cells represents the sac, and the central aggregation the future 
visceral mass. 
It is to be remarked, that at this moment all the cells of the 
nucleus are identical. None of them has become differentiated, 
either in its nature or in its position. In consequence of transfor- 
mations that I have been able to follow step by step, and which 
will be described in detail in a memoir of which these notes are only 
a precursor, we see successively formed in the nucleus all the parts 
of the adult Sacculina. In the peripheral layer the cells increase 
in number, those of the margins become elongated radially, anasto- 
mose, and form sheaves of connective tissue; the more central ones 
become elongated and anastomose tangentially, and form muscular 
fibres. In the central aggregation the peripheral layers undergo an 
analogous transformation to form the wall of the visceral mass; of 
the interior cells some become elongated and anastomose to form 
the transverse muscular planes, while the others, arranged in two 
symmetrical groups, remain rounded and furnish the ova, as well 
as the testicular cells. 
Before these modifications are completed we observe the forma- 
tion, in the portion of the cavernous tissue which separates the 
nucleus from the wall of the membrane, of two parallel and con- 
tiguous planes of cells, placed transversely with regard to the axis 
of the crab. These cells soon secrete between them a plate of 
chitine, which splits. The cleft opens and gives access to the 
nucleus outside the cavity of the tumour in which it was contained, 
The nucleus gradually pushes itself outwards and comes into con- 
tact with the integuments of the crab. Here it still continues to 
enlarge, becoming developed and gradually acquiring the characters 
of the young external Saceulina. Finally, when it has attained the 
dimensions of 2:5—3 millim., it bursts the integuments of the crab 
and presents itself outside. Becoming an external Saceulina it then 
constitutes those young parasites, the smallest that we can see ex- 
ternally under the abdomen of the crabs. The orifice of issue 
soon becomes regular and all trace of rupture disappears ; but in 
the interior of the crab there still remain the sucking-tubes and the 
flattened pit ( fosse) from which the nucleus has issued, and which 
will form the basilar membrane that we have indicated in the 
adult. 
Complementary males.—At the moment when the Sacculina has 
just become external the orifice of its cloaca is closed, and a thin 
chitinous membrane, attached to the periphery of the latter, sur- 
rounds it entirely. Ina little time this pellicle ruptures and re- 
mains adherent only to the periphery of the cloaca. Young Cyprids 
then come, and insinuating themselves beneath it, attach themselves 
by their antenne to the margins of this orifice. The fact is con- 
stant. All the young Sacculinee have Cyprids thus attached to their 
cloaca. They rarely have only one, usually from two to five; and I 
have found as many as twelve. This fact had never before been 
ascertained in Sacculina, nor, so generally, in any Rhizocephale. 
The presence of numerous Cyprids around the cloaca proves clearly 
Ann. & Mag. N. Hist. Ser. 5. Vol. xii. 
