Mr. C. Spence Bate on the Development of the Cirripedia. 331 



First, it assimilates to the appearance of the larva of certain 

 Entomostraca, being liberated from the ovum like them without 

 eyes ; after which it next approaches in character towards the 

 adult Entomostraca, bearing an external resemblance to the bi- 

 valve Crustacea, and like these perfected animals possesses organs 

 of sight, from which period they pass out of recognized tribes, 

 and comprise a family peculiar to themselves. These observations 

 tend to corroborate the now generally received opinion that they 

 are true Crustacea, and among this class they appear to fill up a 

 vacancy which alone was wanting throughout the whole range 

 of the Invertebrata, — I mean a sedentary family, one or more of 

 which exists among each successive race of animals. 



The Polyp, from its analogy to the larva of the Medusa, 

 may be looked upon as representing the sedentary family among 

 the Acalephse, — the fossil Encrinites and the larva of the Coma- 

 tula as representing the same position among the Asterise. The 

 Tunicata among Mollusks and the Serpulse among Annelides 

 appear to hold a similar relation, each to their separate class, 

 as that which the Cirripedia occupy in relation to the Crustacea ; 

 and these last, by the different forms which they pass through in 

 their individual development, may be said to represent the type of 

 those separate forms in the sedentary character. 



It would scarcely be just for me to close this paper without 

 alluding to how much I am indebted to my friend Mr. Jeffreys 

 both for specimens and a knowledge of the different species, his 

 cabinet being as rich in this department of natural history as in 

 that of British Mollusca ; or without expressing my thanks to Mr. 

 Darwin, but for whose kindness I should have been guilty of 

 publishing more than a single error. 



EXPLANATION OF PLATES VI. VII. VIII. 



Fig. 1. Balanus balanoides as it appears when first liberated from the 

 ovum. 



— 2. The same after the first moult ; 2 a, abdominal appendage. 



— 3. The same after the second moult; 3 a, abdominal appendage. 



— 4. The same, lateral view. 



— 5. Balanus perforatus just liberated from the ovum ; abdominal view. 



— 6. The same after the first moult ; abdominal view. 



B. The (so-called) eye. 



C. Abdominal appendage. 



D. Caudal termination. 



E. Proboscis. 



F. Supposed oral aperture which is protected by the lip or 



valve G. 

 II. H. Horns or outer antenna;. 

 K. K. True or interior antennae. 



1 . First pair of natatory legs. 



2. Second ditto. 



3. Third ditto. 



These letters also refer to fig. 14. 



