424 Dr. A. Krohn on the Development of the Girripedia. 



a prominent lens and enveloped in dark pigment, shines through 

 from the interior of the body. This ocellus rests upon tb^ 

 middle of the anterior margin of a distinctly marked structui f 

 closely applied to the ventral surface, and surrounding the oeso- 

 phagus like a ring (PI. VII. fig. 3), which I can regard as nothing 

 but the central mass of the nervous system or as the oesophageal 

 ring. The swimming feet, of which the foremost pair are simple, 

 the intermediate and hinder pairs divided into two branches, 

 are abundantly beset with long bristles, part of which are simple, 

 part delicately plumose (fig. 2). In the middle of the extremity 

 of the proboscidiform process is the mouth, leading into a narrow 

 oesophagus, which extends through the axis of the process, and 

 penetrates into the body through the orifice of the oesophageal 

 ring. The rest of the alimentary canal passes straight through 

 the body, swells in the middle of its course into a roundish dila- 

 tation, and terminates in an anus, situated dorsally at the base 

 of the caudiform appendage (fig. 2) *. 



In the second period of development, the larva, as is well 

 known, is enclosed in a bivalved carapace or shell, in the same 

 way as the genus Cypris. It possesses two compound eyes and 

 one simple one, and is furnished on the lower surface of the 

 hinder part of the body, corresponding with the thorax of the 

 mature animal, with six pairs of swimming feet divided into two 

 branches. At the extremity of this region of the body there is 

 a short tail-like process (abdomen of Darwin), which is furnished 

 with two appendages resembling the branches of the swimming 

 feet. Two other strongly developed members are particularly 

 worthy of notice ; these spring from the fore part of the body, 

 in the vicinity of the compound eyes. With their assistance 

 the larva creeps about, and it is by means of them that it finally 

 attaches itself to foreign bodies, when the time has arrived for 

 its last metamorphosis f. 



The two compound eyes lie quite laterally close under the 



* Leaving out of consideration the horns of the carapace and the spinous 

 process, the larvae of the Cirripedes consequently agree closely, both in 

 their external and internal structure, with the young forms of the Cyclo- 

 pidce, as these are made known to us by the admirable memoir of Claus 

 (On the Anatomy and Developmental History of the Copepoda, Wieg- 

 mann's Archiv, 1858, p. 1). This agreement shows itself not only in the 

 similar number and analogous nature of the swimming feet, but also in the 

 structure of the eye (see Claus, I. c. figs. 64 & 66), in the arrangement of 

 the alimentary tube, and in the presence of a so-called oral hood (Mund- 

 kappe), which is to be compared with the proboscidiform process. But the 

 caudiform appendage of the Cirripede-larvae corresponds with the poste- 

 rior segment of the Nauplius-fovm of the Copepod-larvse, as will appear 

 hereafter. 



t Upon this period see the extremely accurate and complete description 

 of Darwin (vol. li. pp. 110-123). 



