Mr. C. Spence Bate on the Development of the Cirripedia. 327 



being a feature peculiar to this stage of the larva of the Cii'ripedia, 

 among which it differs in length and size according to the species ; 

 like the caudal appendages, it increases in length, together with 

 the natatory legs, with each of the earlier successive moults. At 

 the base of this organ I have observed an irregular pulsation, 

 and consequently presume it to be the seat of the heart. 



At the shoulders of the anterior extremity extends right and 

 left a small process, which under a one-fourth of an inch object- 

 glass appears to terminate most commonly in a bitid extremity ; 

 but through the assistance of a higher power than I have used, 

 I am informed by Mr. Darwin that this appearance is shown to 

 be erroneous, it being seen to terminate always in a point : 

 these are attached to the lower surface of the shield, and after the 

 first moult appear to consist of two articulations ; they may differ 

 in dimensions in respective species, but, as far as I have had an 

 opportunity of observing, are universally present in the sessile 

 division of the Cirripedia; and judging from the figure given by 

 Burmeister in his memoir upon the pedunculated Cirripedia, and 

 those by Mr. Thomson upon the same division, they appear to 

 be constant throughout the whole class, and probably are, as 

 stated by Burmeister, homologous with the antennae ; and if so, 

 they must represent the external or superior pair ; but in watch- 

 ing the habits of these young creatures I have seen nothing 

 which can induce me to accept the idea that they are made use 

 of by the animal, as he presumes, for the purpose of climbing or 

 holding itself m contact with any foreign body. In order to fulfill 

 these conditions the more perfectly, they each terminate with 

 a hook in Burmeister's figure ; but this, not being represented 

 in Thomson's, whose obsenations, in most essentials, coincide 

 with those which opportunity has placed within my reach, in- 

 duces me to receive the former author's drawing of these an- 

 tennae with caution, although it is probable that he may be 

 correct when he presumes that they become the perambulatory 

 feet in the pupa ; and if so, we have an interesting exemplifi- 

 cation of the assumed fact, that the antennae among animals are 

 but less modified in order to fulfill certain peculiar conditions ; 

 thus they represent in one stage organs of sense, whereas in the 

 next they fulfill the conditions of true feet. Besides these horns 

 or outer antennae, the larva is endowed with a smaller pair of 

 simple structure, more typical of those organs in Crustacea, and 

 which, therefore, must represent the internal or inferior pair; 

 but these I have not been able to observe previous to the shed- 

 ding of the first exuviae, though ]\Ir. Darwin has been so kind as 

 to inform me that he has seen them at that early period in the 

 larva of ScapeUum vulgare, and Prof. Goodsir has also figured 

 them from the larva of Balanus Tintinnabulum ; therefore from 



