424 Miscellaneous. 
fact that no Sacculine are to be found of a less size than about 
3 millim. I have examined several thousand infested crabs without 
ever finding a smaller Sacculina. The embryogeny of Sacculina and 
of the other Rhizocephala not being known, one could only form 
hypotheses as to their development; and the hypothesis generally 
accepted is that the Cypridian larva of the parasite attaches itself 
by the head to the abdomen of the crab, loses its limbs, and insinu- 
ates into the tissues of its victim a part of its head, from which 
spring tubes which invade the whole of the crab. MM. Giard has 
even gone so far as to specify the facts, asserting that the parasite 
was formed during the copulation of the crabs. If this was true 
the fact that I have pointed out would be truly inexplicable, for 
between a Sacculina of 3 millim. and a Cypris of not more than 0°2 
millim. in length there is a whole series of intermediate states which 
ought to be found. Moreover the smallest Sacculine are already 
like the adults, and have nothing in common with an active animal, 
or even with one capable of locomotion. How, then, could the para- 
site come thus completely formed from without? The answer is 
easy. It does not come from without, but from within. Before 
showing itself externally the Sacculina already exists in the abdo- 
men of the crab, between the intestine and the wall of the body. It 
exists thus complete, with its sac, its ovaries, its accessory glands, 
its testes, and its nervous system, and it is only by increasing in size 
that it produces by compression necrosis of the integuments of the 
crab, thinning and finally rupturing them to break through to the 
outside. 
In the youngest state in which one can find it, the anternal Sac- 
culinu consists of a membrane in the form of a flattened sac, stretched 
between the intestine and the abdominal wall of the crab in the 
general body-cavity, in the midst of a cellulo-adipose tissue. From 
the whole of its surface, but especially from its irregularly sinuous 
margins, issue tubes which, even at this period, have completely 
invaded the crab. The wall of the membrane is clothed with a 
thin chitinous layer and formed of large cells with voluminous 
nuclei, The interior is formed of stellate cells, the processes of 
which, anastomosing with each other, convert the whole into a sort 
of cavernous connective tissue, the innumerable cavities of which all 
communicate with one another. The large parietal cells are con- 
tinued into the tubes. In its median region the membrane, instead 
of remaining thin, becomes suddenly thickened, and forms a sort of 
tumour upon its surface. In the midst of the abundant cavernous 
tissue which fills this swelling there is a spherical aggregation of 
small cells, to which I give the name of nucleus. The “coll s of the 
nucleus are arranged so as to form a central mass, separated by a 
narrow space from an enveloping layer. At this period the entire 
Sacculina is not more than + millim. broad; the nucleus is hardly 
0-05 millim. in diameter ; and yet every thing that will constitute 
the adult Sacculina is represented in it. The membrane, with its 
cavernous tissue, will form the basilar membrane ; the nucleus will 
form the eaternal Sacculina; in this nucleus the spherical layer of 
