326 Mr. C. SpenceBatc on the Development of the Cirripedia. 



them, particularly if the homologies as pointed out by Burmei- 

 ster be correct, to be identical ; an idea which receives support 

 from the gradual receding of the spot from the anterior edge, 

 near which it may be observed in the larva previous to the first 

 moult ; whereas in the next it is further back, and in the third, as 

 given in PI. VI. fig. 3 b, the only specimen of which I have had an 

 opportunity of observing, it has considerably receded, being in a 

 line with the extremity of the probosciform organ. Therefore, 

 presuming such to be the case, I can scarcely appreciate the idea 

 advanced by this latter author, that the two large eyes in the pupa 

 are formed by the splitting into halves of this centi'al spot ; or, 

 to translate his own words, " that the single eye is compounded 

 of two halves, which, by degrees, separate more and more until in 

 the following period they are divided by a considerable space." 



In this description their development is not analogous to that 

 of the eyes in the larva of the Entomostraca, which certainly in 

 this stage must be considered as its nearest ally. For instance, 

 in the larva of Chirocephalus diaphanus the two lateral organs of 

 vision are apparent previous to the disappearance of the " central 

 eye," plainly showing that the real eyes are not developed from 

 the central spot, whatever it may be. 



Among the more peculiar features of the larvae of these animals 

 is the presence of an elongated forked process of the abdomen, 

 forming to all outward appearance a second caudal appendage, 

 and which has been confounded with the tail in Prof. Goodsir's 

 figure and desci'iption of the larva previous to the first moult, 

 where he says, ^^the last segment is armed with three sharp 

 strong spines which project backwards." After the first moult 

 tliis appendage increases in length, greater or less in different 

 species, by the addition of another ring proceeding from the 

 extremity of the last, and like it terminating in a similarly forked 

 extremity. Of its uses in the larva, or its homology in the adult 

 animal, I have not been able to satisfy myself; but it is a fea- 

 ture in a more or less modified form (as far as I have observed) 

 universally present in this early stage of their development. 



In Balanus perforatus, Clitia Stj'omia, and Chthamalus depressus, 

 the growth of the caudal appendages increases at the first moult 

 to a length much greater in proportion than the same organs do 

 in Balanus halanoides. 



Another organ equally constant and peculiar to the early larval 

 stage of these animals is, that which for convenience of commu- 

 nication I shall call a proboscis. This, the animal has the power 

 of raising and lowering at pleasure, as its uses may require. 

 At its extremity appears to be an oral-like aperture which is 

 closed by a valve or upper lip. This organ, as far as my know- 

 ledge goes, has no analogous representation among Crustacea, it 



