THE THTEOSTEACA. 



43 



1883. Lepas pectinata, Hoek, ''Challenger' Cirripedia, Reports, vol. viii. p, 40. 

 1891. Lepas pectinata, Gruvel, Contr. il Tetude des Cirrhipedes, p. 114, pi. 28. 

 1899. Lepas pectinata, Hansen, Die Cladoceren und Cirripedien des Plankton-Expedition, p. 33. 



Darwin states that be had examined the pupa of Lepas pectinata, and found the 

 surface of the carapace " marked with curious points of various shapes, often star-shaped, 

 in parts reticulated, and confluent along the dorsal margin, and in parts lined." Under 

 the heading " Acoustic Organs," he says, " these lead, as described in my former volume, 

 into a sack, with a bag suspended in it, which is provided with a large nerve, and which 

 I believe to be the acoustic vesicle. These orifices occur in the carapace, either in the 

 same position or a little more posteriorly, in the pupae of all Cirripedes. In Balaiius 

 balanoides they are minute, being only oifduth [of an inch] in diameter, but are surrounded 

 with a border : in Conchoderma viryata they are also surrounded by a border : in Lepas 

 pectinata the orifices are einroth of an inch in diameter, and are very singular from 

 being seated on rounded prominences, causing the carapace to have two short, blunt 

 horns in front." Influenced by the knoT\Ti position of acoustic appai'atus in the higher 

 Crustacea, Darwin supposed that these orifices might represent the otherwise miissing 

 anterior antennae in the j)uj)al Cirripede. 



On the other hand, M. A. Gruvel, in discussing the Cypris-\ax\s. of L. pectinata says 

 that " its valves carry at the lower part a sort of strong horn, corresponding to what will 

 be the adductor muscle of the valves in the adult" {loc. cit. p. 115). He maintains for 

 the Thyrostracan group at large that " hearing has no special oi-gans, since this sense 

 does not exist in the Cirripedes." He bases his conclusion on experiments that seem 

 fairly conclusive for the adult stage, but he does not claim to have observed the effects of 

 them upon larval forms, which would indeed he a matter of considerable difficulty 

 (pp. 55, 179). M. Gruvel gives highly magnified figures of the valve-markings in the 

 Cijpris of L. j^ectinata, oi which he says that, rou^ghly speaking, the ornamentation of 

 the transparent carapace is formed of regularly arranged polygonal thickenings of the 

 cliitin, the hexagons or pentagons being marked off" by narrow chitinous ribs. This 

 reads like a very different account from Darwin's. But Darwin accurately describes the 

 appearance under a low magnification, whereas every successive enlargement changes the 

 pattern, but on the whole produces the impression of more and more uniformity, as the 

 details in different parts of the valve are more clearly made out. 



The single specimen of this Cf/pris-\avya, in the present collection measured 1'25 mm., 

 or a twentieth of an inch. When the valves were opened the organs within were no longer 

 soft, but dry and unyielding. In lateral view, as shown in fig. 3, p. 4Ji, the shape of the 

 carapace is rather striking, from the great height of the rounded upper half, in contrast 

 with the triangular distal portion, \vhich narrows rapidly to the acute apices. The 

 greatest height is rather more than half the length. About a third of the length from 

 the front, and a little nearer the ventral than the dorsal margin, the dark compound eyes 

 are situated. The ventral margins are for the most part straight and nearly parallel, 

 but not accurately adjusted one to the other, indicating a want of symmetry between the 

 valves, as noted by H. J. Hansen {loc. cit. p. 33) for what he supposes to be the pupa of 



SECOND SERIES. — ZOOLOGY, VOL. X. 8 



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