20 CIRRIPEDIA, 



to Von Baer's definition ; for, to take as an example the eyes 

 of a Cirripede, — as seen in the first larval stage, there is only 

 one eye, and that most simple; in the pupa there are two, both 

 compound, and furnished with complicated muscles; lastly, 

 in the mature animal there are still two, but of very 

 minute size, often almost confluent, and of the simplest 

 structure; hence, then, there has been much morphological 

 differentiation, but it is almost a contradiction in terms to 

 speak, in relation to such a case, of perfection of type ; and 

 what has happenend to one organ, might happen to other 

 organs, and so to the whole animal. Lastly, under a phy- 

 siological point of view, and taking the Balanidse as the 

 most perfect type of the class, the sub-cesophageal portion 

 of the nervous system is highly concentrated ; the organs of 

 sense, excepting the eyes, seem more largely developed than 

 in ordinary Crustaceans ; the circulating system is of the 

 simplest kind, being only lacunal ; special Branchiae, how- 

 ever, are developed by the metamorphosis of, as T believe, 

 a special organ, occurring only in the Lepadidae ; the di- 

 gestive organs are very simple, from not having any distinct 

 liver ; the generative system is very low, for both sexes are 

 generally united in the same individual ; and the testes and 

 ovaria closelv resemble each other. On the other hand, 

 the thoracic limbs are, to a considerable extent, specialised 

 in their structure and functions ; only the three posterior 

 pairs strictly resembling each other. Lastly, the der- 

 mal and muscular systems are complicated, and not, to use 

 Professor Owen's term, by mere vegetative repetition, as 

 will be obvious to any one who will study the beautifully 

 constructed and modified carapace — that is the operculum, 

 shell and basis -of a Balanus. On the whole, I look at a 

 Cirripede as a being of a low type, which has undergone 

 much morphological differentiation, and which has, in some 

 few lines of structure, arrived at considerable perfection, — 

 meaning, by the terms perfection and lowness, some vague 

 resemblance to animals universally considered of a higher 

 rank. 



It has been seen that I divide the Cirripedia into three 

 orders, — the Thoracica, Abdominalia, and Apoda ; between 



