Dr. A. Krohn on the Development of the Cirripedia. 423 



LIII. — Observations on the Development of the Cirripedia. 

 By Dr. August Krohn*. 

 [With a Plate.] 

 The results which we have lately obtained — thanks to the labours 

 of Burmeisterf, Spence Bate J, and Darwin § — upon the develop- 

 ment of the Cirripedia are so satisfactory, that we might already 

 congratulate ourselves upon an insight into the manifold changes 

 passed through by the young animal from its birth to the attain- 

 ment of its perfect form, if there were not a sensible gap still 

 vacant. It is still unknown by what intermediate steps the 

 larva, which, during the first period of its development, agrees 

 in so many respects with the young forms of the Entomostraca, 

 especially the Copepoda, passes to the subsequent Cypris-\ike 

 form. During my residence in Funchal, and afterwards at 

 Messina, I was able to obtain some information upon this still 

 unexplained point. Before communicating my observations on 

 this subject, I think it will be necessary in the first place to describe 

 the form presented by the larva during the first period of its 

 development, and then to refer more particularly to individual 

 organs which are peculiar to it in its later Cypris-form. 



At a certain stage of development, when the larva has moulted 

 two or three times after its escape from the egg f we distinguish 

 in it a broad body ( Vorderleib), frequently truncated in front, and 

 diminishing posteriorly, followed by two slender processes extend- 

 ing backwards (PL VII. fig. 1). The superior process has the 

 form of a straight, extended, and often very long spine ; the in- 

 ferior one, which is stouter, runs, gradually tapering, to a forked 

 extremity, and is, especially in the later stages, capable of being 

 bent and extended. I characterize it provisionally as the caudiform 

 appendage ||. The body is covered on the dorsal surface with a 

 carapace or shield, the anterior angles of which are produced 

 into two thin horns, furnished with a few curved bristles at the 

 apex % . On the lower surface the body is provided with three 

 pairs of swimming feet, and with a proboscidiform process spring- 

 ing freely from the middle between the last pair. Close behind 

 the anterior margin of the carapace, a small eye, provided with 



* Translated from Wiegmann's Archiv, 1860, p. 1, by W. S. Dallas, 

 F.L.S. 



f Beitrage zur Naturgeschichte der Rankenfiisser, 1843. 



X On the Development of the Cirripedia, Annals, ser. 2. vol, viii. p. 324, 

 1851. 



§ Monograph of the subclass Cirripedia, 1851 & 1854. 



|| From the figures to Spence Bate's memoir, I cannot but think that 

 this observer regards the spinous process as a prolongation of the carapace 

 next to be mentioned, which is certainly wrong. 



H Burmeister and Darwin regard these horns as antennae, but erro- 

 neously, as will hereafter appear. 



