106 BALANID^E. 



tennae are amongst the earliest developed organs ; and as 

 the first pair of natatory legs (PI. 29, figs. 8 — 10, e) in 

 these Cirripedial larvae, might so very naturally be thought 

 to be antennae (as has been remarked to me by Mr. Dana), 

 both from their structure and from their position a little 

 anteriorly to the mouth, I am well aware that to prove my 

 view correct, namely, that these horns are the second pair 

 of antennae in process of formation, it is not sufficient merely 

 to have seen organs resembling antennae within them j nor 

 is it sufficient to advance the strictly analogical fact of the 

 first- mentioned pair of antennae, which in Scalpellum in- 

 disputably appear in their earliest condition within an en- 

 velope or horn. Further evidence is required, and this is 

 presented in Cryptophialus, in which the lateral horns of 

 the egg-like larva, in its first stage (PI. 24, fig. 16), can be 

 actually followed step by step until, in the second stage 

 (fig. 17), just before passing into the pupa, the horns are 

 seen to have become larger and more nearly approximated 

 to each other on the ventral surface ; and whilst in this con- 

 dition, I several times dissected out the prehensile antennae 

 of the future pupa with every character perfectly recognisable. 

 Hence I cannot doubt that in the larvae of Cirripedes the 

 law of development is, that in their very earliest condition, the 

 small first pair of antennae are enclosed in cases ; and that 

 the large second pair remain thus enveloped until the pupal 

 stage. This conclusion, we shall immediately see, is in 

 harmony with the late development of the succeeding 

 appendages or organs of the mouth, which certainly do not 

 appear in the first larval stage, and are not known to 

 appear even till after the final metamorphosis.* 



The mouth is more or less probosciformed (PI. 29, 

 figs. 8 — 10, d), differing considerably in this respect in dif- 

 ferent species of the Lepadidae ; and this, probably, is due 

 to the larva being born in a more or less mature condition. 

 Its exact position likewise varies, for it arises either between 

 the first or second pairs of natatory legs. It is known, from 



* According to It Joly, ('Annales des Sciences Naturelles,' 2d series, 

 torn, xix, p. 59) in the larva of the macrourons Caridina, the natatory legs 

 appear before the gnathites or parts of the mouth; so that in ordinary Crus- 

 taceans there is no invariable order of development from the anterior towards 

 the posterior end of the body, as has sometimes been supposed. 



