1318 



CRUSTACEA. 



the segment behind. We state beyond a reason for considering this 

 segment the basal portion of the anterior antennae. 



The margin of the large anterior portion in the Caligidae is aided 

 in attaching itself in two ways, which may occur either separately or 

 together. These are, 1, minute spinules ranging along a line parallel 

 with the lateral outline, often in colourless species near the inner limits 

 of the narrow transparent margin of the body (fig. 1 h, r, Plate 93) ; 

 2, sucker-like disks fitted expressly to affix the body to the surface on 

 which it may rest. There are often two of these sucker-disks on the 

 anterior margin, and they have been mistaken for eyes ; one is repre- 

 sented enlarged, in the figure just referred to. They vary from a cir- 

 cular to an elliptical form ; and are thin fleshy disks, attached by their 

 central portions. Posterior to the first pair of antennae in the Cali- 

 gidse and opposite the second pair, there is often a second disk, either 

 side j and sometimes a third exists near the latero-posterior margin. 



Besides these means of affixing itself, independently of the regular 

 appendages, there is in the young forms of some species, a slender 

 organ, proceeding from the middle of the front, which ends in a small 

 disk. In some species the stem is quite slender. The genus CMlimus 

 is based on the presence of this organ. But Kroyer has shown that 

 this organ is not a proper basis for a genus,* and the same view is more 

 recently sustained by Dr. Fr. Muller.f In 1838, the author, in an 

 account of the Caligus Americanus,J described the same appendage as 

 occurring sometimes in this species. Plate 93, figures 1 u, v, w, re- 

 present its appearance in different states, lu represents an upper 

 view of the front of the animal, just before a change of skin ; c, d, is 

 the front of the Caligus; e,f, the front of the inner new-formed shell; 

 m, n, o, the appendage. In 1 v, the appendage n, m, o, is seen m 

 profile, the corresponding parts being lettered alike in 1 u, and 1 v. 

 In 1 w, the same appendage is represented, with the outer shell of the 

 animal removed, and the organ drawn forward. In one instance, the 

 author observed an animal having the appendage situated as in 1 vo, 

 except that it consisted of three of these appendages placed end to 

 end ; and probably it was formed at three successive moultings. In 

 external appearance, this organ much resembled a muscle, as it was 

 striated like them, though very coarsely. 



* Tids., ii. 1837. f Archiv fur Naturgeschichte, 1852, 91. 



J Amer. J. Sci., vol. xxxiv, p. 225. 



