•w 



April 1, 1S6S.J 



HARDWICKE'S SCIENCE-GOSSIP. 



79 



longiconte, and other marine Crustacea which beat 

 the mud in search of worms. Our larvae are very 

 pugnacious ; they are continually butting at one 

 another, after the manner of rams ; and when one 

 commences an assault, the spectators are certain to 

 join in it. No perceptible wounds result from these 

 encounters ; but probably in the case of weak in- 

 dividuals the results are more fatal, or how are we 

 to account for th3 constant decrease in the number 

 of specimens? I am loth to affix the stigma of 

 cannibalism on my favourites, but how shall we 

 escape the inference ? 



During the two months the larvae have been in 

 confinement there has been no change into the pupa 

 or imago states. Do [they continue through the 

 winter in the larval condition? The vessel con- 

 taining them is covered with a plate of glass, so 

 that there can be no doubt about it. Indeed, I 

 have been most anxious to trace the succeeding 

 changes, and make acquaintance with the perfect 

 Corethra plumicornis. 



the base, and then branching into two, four, or even 

 eight processes (fig. 52). Entering the base of one 

 of them, I traced a nerve filament, so that their 

 function may be tactile. 



Anal Segment. — Terminating the body we find 

 four small branchial leaflets, above them four 

 plumose bristles, and below, inserted on each side 

 of the rectal opening, two hooked claws (fig. 57, d,f). 

 What can be the use of these hooks which point 

 forwards, and curve beneath the segment ? Perhaps 

 they are designed to fix the larva before its trans- 

 formation. Along the midline of the underside of 

 the tail (fig. 57, g) is inserted a fan-shaped cluster 

 of bristles, bifurcate at the base, and delicately 

 plumed (fig. 51). This structure, in fact, resembles 

 a feather fan, and serves at the same time as a 

 helm, and powerful scull. It is the motive organ of 

 the larva, and forms a beautiful microscopic object, 

 reminding us of the heterocercal tails of some fish. 



Head (fig. 50, a). — The head is divided from the 

 thorax by a well-marked constriction. It is corn- 



Fig. 53. 



Fig. 51. Fig. 52. 



Fig. 50. Corethra plumicornis x slightly, a. Head. b. Thoracic air-cells, c. Abdominal 

 air-cells, d. (Esophagus, e. Gizzard. /. Stomach, g. Commencement of intestine 

 and origin of four biliary ducts, h. Colon, i. Fan-like anal flu. k. Four bronchial 

 leaflets. /. m. Dorsal vessel. 



Fig. 51. Lower part of hair from tail fan. Fig. 52. Compound hairs from the body. 



Fig. 53. a. Eye, x 30. b. Single lens, and three detached lenses, showing the way in 

 which they are imbedded in the pigmentary layer ; beneath are the fibres of the optic 

 nerve, x 150. 



General Characters.— -The body is about half an 

 inch long (fig. 50), cylindrical, and gradually tapering 

 to the tail ; there are no feet or other appendages, 

 except those attached to the anal segment, which 

 will be described presently. The outline of the 

 body is not straight, but somewhat /-shaped. The 

 third segment is broadest and most prominent, and 

 contains two air-sacs, which shine like globules of 

 mercury ; and again we find it slightly humped at 

 the ninth segment, which in like manner encloses two 

 air-sacs (fig. 50, b, c). The skin is delicate, perfectly 

 smooth, and pitted over with round translucent dots. 

 On the sides of the segments are scattered com- 

 pound hairs. These hairs are peculiar, simple at 



pressed laterally, so that seen from above it appears 

 wedge-shaped, and the frontal portion is prolonged 

 into a kind of snout. The parts composing the 

 mouth are so different from the ordinary types, that 

 I shall leave it to others to determine them, and 

 merely enumerate the organs from before back- 

 wards. 1st. Depending from the apex, we find two 

 large processes which seem to be modified antenuaj 

 (fig.54,#) ; they are two-jointed, the lower terminated 

 by four acuminate claws. 2nd. A bundle of ten 

 needle-like curved lancets (mandibula ?) (fig. 54, h). 

 3rd. Posterior to these, two minute, half-ovate 

 plates, serrate in front (fig. 54, c). 4th. A spoon- 

 like process, articulated transversely, and acting as 



