CRUSTACEA. 409 



The two typical divisions of the Copepocl maxillipeds are present, viz. an 

 outer and anterior larger division, and an inner and posterior smaller one. 

 The first pair of thoracic feet, as is usual amongst Copepoda, is attached 

 to the cephalo-thorax. It has not the typical biramous Copepod character. 

 There are four free segments behind the cephalo-thorax, the last of which 

 ends in a fork. Three of them bear appendages, which are rudimentary in 

 this early larval stage. On the dorsal surface are present paired eyes as 

 well as an unpaired median eye. 



Between the larval condition and that of the adult a number of ecdyses 

 intervene. 



ClRRIPEDIA. 



The larvae of all the Cirripedia, with one or two exceptions, leave 

 the egg in the Nauplius condition. The Nauplii differ somewhat in 

 the separate groups, and the post-nauplial stages vary not incon- 

 siderably. 



It will be most convenient to treat successively the larval history 

 of the four sub-orders, viz. Thoracica, Abdominalia, Apoda, and Rhizo- 

 cephala. 



Thoracica. The just hatched larvae at once leave the egg lamellae 

 of their parent. They pass out through an opening in the mantle 

 near the mouth, and during this passage the shell of the parent is 

 opened and the movements of the cirriform feet cease. 



The larval stages commence with a Nauplius 1 which, though re- 

 garded by Glaus as closely resembling the Copepod Nauplius (figs. 231 

 and 232 A), certainly has very marked peculiarities of its own, and in 

 some respects approaches the Phyllopod Nauplius. It is in the 

 youngest stage somewhat triangular in form, and covered on the 

 dorsal side by a very delicate and hardly perceptible dorsal shield, 

 which is prolonged laterally into two very peculiar conical horns (fig. 

 231 Hi), which are the most characteristic structures of the Cirriped 

 Nauplius. They are connected with a glandular mass, the secretion 

 from which passes out at their apex. Anteriorly the dorsal shield 

 has the same extension as the body, but posteriorly it projects slightly. 



An unpaired eye is situated on the ventral surface of the head, 

 and immediately behind it there springs a more or less considerable 

 upper lip (Ib), which resembles the Phyllopod labrum rather than that 

 of the Copepoda. Both mouth and anus are present, and the hind end 

 of the body is slightly forked in some forms, but ends in others, e.g. 

 Lepas fascicularis, in an elongated spine. The anterior of the three 

 pairs of Nauplius appendages (At ') is uniramous, and the two posterior 

 (At* and md) are biramous. From the protopodites of both the latter 

 spring strong hooks like those of the Copepod and Phyllopod Nauplii. 

 In some Nauplii, e.g. that of Balanus, the appendages are at first 



mode of interpretation would bring the appendages of Argulus into a much closer 

 agreement with those of the parasitic Copepoda. It does not seem incompatible with 

 the existence of the stylet-like maxillae detected by Claus in the adult. 



1 Alepas squalicola is stated by Koren and Danielssen to form an exception to this 

 rule, and to leave the egg with six pairs of appendages. 



