258 



THE ANATOMY OF IXYERTEBRATED ANIMALS. 



needles in a watch-glass full of sea-water, one is pretty sure 

 to be found whence a number of active little JVaiqrfius -like 

 animalcules are set free (Fig. 68, A). Each presents a some- 



Fig. 68.— A. Larva of Balanus balanoides on leaving the egs (after Spence-Bate). 

 B. Attached pupa of Lepas Australis (after Darwin): n, antennary apodemes ; t, 

 gut-formed gland, with cement-duct running to the antenna. 



whit triangular body, produced in the middle line posteriorly 

 and at its anterior lateral anp-les. The mouth is situated on 

 a proboscidiform projection placed nearly in the centre of 

 the body, and in the midst of three pairs of natatory limbs, 

 of which the two posterior pairs have bifid extremities. In 

 front of the mouth, either in this stage, or after one or two 

 moultings, two filaments are often developed. A single eye- 

 spot is situated in front of the bases of the anterior append- 

 ages. After moultino; several times the larva assumes a 

 new form, passing into its second stage. The carapace is 

 now oral and compressed, so as more nearly to resemble that 

 of a Daphnia or Gypris. There are two eyes. The first 

 pair of swimming appendages of the Nauplius are converted 

 into antenniform organs, each provided with a sucker, and 

 the rudiments of the six pairs of cirri make their appearance 

 behind the mouth. 1 



In the third stage, the larva is, as Mr. Darwin states, 

 " much compressed, nearly of the shape of a Cypris or mus- 

 cle-shell, with the anterior end the thickest, the sternal sur- 

 face nearly or quite straight, and the dorsal arched. Almost 

 the whole of what is externally visible consists of the cara- 



1 According to Claus (" Grundziige der Zoologie," 3te Auflage, p. 460), the 

 second pair of appendages disappears, and the third gives rise to the mandi- 

 bles. In this case the antennary organs represent antennules, and the limbs 

 of the Cirripede Nauplius correspond with those of the Copepod and Branchi- 

 opod Nauplius. 



