48 Dr. F. Miiller on the Rhizocephala, 



is but slightly developed ; the golden crown in the interior of 

 the host (fig. 6, k) differs from that of Lernaodiscus in that single 

 broad branches issue from the ring, the wide ramifications of 

 which gradually pass into the thinner skin of the head, whilst 

 Lernceo discus has acute and distinctly circumscribed teeth. The 

 roots shooting from the head extend backwards upon the left 

 side of the Pagurus, and form, between the hepatic tubes, a 

 dense tuft of tubes springing from a few principal stems. From 

 this tuft the hepatic tubes passing through it may easily be ex- 

 tracted, and it may thus be completely isolated (fig. 4B, i^). 

 The colour of the tuft of roots is dark grass-green ; it shines 

 distinctly through the thin wall of the body of the Pagurus. 



The larvae of the two parasites have so many points of agree- 

 ment, that I describe only that oi Lernaodiscus, and shall merely 

 call attention to the differences presented by that of Sacculina. 



The larva of Lernceodiscus (fig. 6) is 0*2 millim. in length, 

 0"12 millim. in breadth anteriorly, and diminishes at first 

 slightly, but in the last third more rapidly. At the posterior 

 extremity it bears two short points. The slightly arched ante- 

 rior margin runs out on each side into a short horn, somewhat 

 bent backwards at the apex. The back is covered by a carapace 

 which extends beyond the body in front and at the sides by 

 0*04 to 0*05 millim. ; posteriorly it scarcely covers the origin of 

 the two points, and also conceals only the base of the horns of 

 the frontal margin. 



On the lower surface there is, at a short distance from the an- 

 terior margin, a large, somewhat transverse eye, usually slightly 

 emarginate in front, from which a strong nerve may be traced 

 backwards, but which appears to be destitute of a refractive 

 body. I cannot see the bristles at the sides of the eye to which 

 Max Schultze has called attention in the young Cirripedia. 



The point of origin of the three pairs of feet is situated nearly 

 in the middle between the median line and the lateral margin ; 

 the foremost originates close behind the eye, the hindermost at 

 the end of the second fifth of the length. The foremost has a 

 thick cylindrical basal joint, and a short terminal joint with two 

 long bristles ; the second bears upon a thick basal joint a long 

 outer (and anterior) branch with five, and a shorter inner one 

 with three, long bristles ; the third pair of feet is considerably 

 shorter and weaker than the second ; its outer branch bears four, 

 and its inner one two, long bristles. The longer branches are 

 annulated, but not distinctly jointed. 



Between the feet of the middle pair there springs a triangular 

 rostrum, with its apex directed backward. The wide intestinal 

 canal, which advances forward a little beyond the rostrum, is 

 still, during the first days, densely filled with brown yelk. Be- 



