STRUCTURE OF LERNEOPODA DALMANNI. 81 



cal portions of the arms lie, is at right angles to the long axis of this space, it is 

 impossible to draw the bar and claspers out without dissecting away the wall of 

 the cavity. 



We have already mentioned, that M. Edwards has seen reason to think, that 

 owing to the elongated cephalo-thorax, and the existence of posterior abdominal 

 appendages, this parasite possesses characters which hardly permit it to be classed 

 along with the other known Lerneopoda. To these we may add the very im- 

 portant one, that the arms are not united at the tip. For although they are in 

 close apposition by the flat surfaces of. their clasper-lil^e terminations, yet the 

 parasite, when removed from the fish to which it is attached, can spontaneously 

 withdraw one or other arm, or both, from the transverse cartilaginous-like bar, 

 so as to separate the claspers completely from each other. After withdrawing 

 the claspers from the bar, the animal does not appear to possess any power of 

 re-attaching them to it. This character of ready separation of the ends of the 

 arms from each other would also prevent us from placing the animal, as has been 

 suggested by M. Edwards, in the genus Brachiella. 



Projecting from each side of the cephalo-thorax, immediately in front of the 

 root of each arm, is a well-marked bulb-like protuberance, noticed both by Retzius 

 and Kroyer, and termed by them the eye-like spots, although, from their colour 

 and structure, they do not consider them to be eyes (fig. 3, a). Each has the ap- 

 pearance of a segment of a sphere. Through the semi-transparent integument of 

 the most prominent part, a quantity of reddish-brown granules, aggregated in elon- 

 gated masses, may be seen. Low magnifying powers also enabled us to detect a very 

 peculiar rod-like structure, connected apparently to the deep surface of the eye- 

 like spot. It commences in a slightly dilated bulb-like part, which passes back- 

 wards and outwards, around the base of the arm on its own side, and terminates 

 in a dilatation similar to that by which it commences. The exact structures to 

 which it is connected at its two ends we cannot say with certainty ; but it is 

 probable, from its position, that it may act as a sling for the support of the base 

 of the arms. The rod has a diameter of st oth of an inch, the bulb of risth. Its 

 structure is characteristic, so that it can at once be distinguished from the sur- 

 rounding parts. It possesses an axial portion, which is about one-third the dia- 

 meter of the entire rod. Under high magnifying powers this presents a corrugated 

 aspect, which reminded us of the well-known appearance of the coagulated medul- 

 lary sheath of a nerve fibre. Surrounding this axial structure is a very trans- 

 parent substance, which has many of the microscopic characters of chitine. 



The abdomen is iVths of an inch long, r\ths broad. It ends posteriorly in a 

 rounded elevation on each side, between which is a depression, so that it possesses 

 an inverted heart-shaped form (fig. 1, c ; fig. 2, b). It is slightly convex on the 

 dorsal, almost flat on the ventral aspect. It has an imperfectly defined segmented 

 appearance, owing to the existence of three circular depressions in the chitinic in- 



VOL. XXIII. PART I. z 



