1884. ] The Crab Parasite, Sacculina. 227 
youngest or so-called Nauplius stage of another Sacculina, S. 
purpurea, It is a free-swimming, active larva, has neither eyes 
nor mouth; its “cypris” and pupa stage, differs from the same 
of the near allied barnacles by the absence of the paired eye on 
the ventral surface of the head, Fig. 4. 
In another later paper? I have described and figured the “ em- 
bryo” of the Bopyrus infecting the common prawn, calling that 
“embryo” the highest and most advanced stage in the develop- 
ment of Bopyrus, which, under favorable circumstances, will 
enter the gill-cavity of the earlier developmental stages of the 
prawn, where it, as the prawn advances in growth, will, when a 
female, lose its eyes, both antennz, the uropods, etc.; while the 
pleopods will degenerate into the abdominal lobes and from the 
seventh free segment will bud a pair of legs. What a clumsy and 
helpless creature the adult female Bopyrus is, may be learned from 
the description and illustration given by me in the two journals 
cited. But our Sacculina is much more degenerate, it is the most 
utterly reduced parasite known. Its body is a mere sac (meas- 
ures 23™™ in thickness, 6™ in width and 43™™ in length, figs. I 
and 2), of kidney shape, convex anteriorly, posteriorly concave in 
the middle and filled with a great number of minute eggs. Its 
lower constricted portion is securely attached by a short stem, 
like a barnacle, to the third last segment on the ventral surface 
of the abdomen of (in this case a female) Panopeus herbstii, 
= abdomen, upon dissection, exhibits a large number of 
i tubes, originating from the stem of the parasite and 
buting over and entangling the intestinal tract of the crab, 
S ee enotically absorbing nourishment from the same. Some 
the ie tubes terminate blind, others form delicate plexuses. At 
ish ea constricted portion of the bag we notice a small, round- 
' ikae, y piece, flattened antero-posteriorly. It has some resem- 
' zt i the fog-pipe of a steamer. Its posterior surface is con- 
width erent into seven parts. It measures 13>” in 
Provided 1 in length. Its anterior surface is concave and 
Sac iy its lower half with a minute opening, the sexual ori- 
side, and gaia surface of the sac I presume to be the dorsal 
; Opposite, the concave, I take for the ventral side of 
the 
animal. The upper smaller part, resembling a fog-pipe, is the 
i 
Idem. 
, Aur. 
Naturanisr, Vol. xv1, January, 1882, pp. 5-12. 
