

CIRRIIOPODA. 



693 



free locomotion ; the third is that in which the 

 young becomes encased in a shell, and fixes 

 itself; in l\\e fourth stage, the young gradually 

 assumes the characters of the adult; ihe fifth 

 stage is that of perfect development. 



First stage. The egg. Its outer covering 

 is a very delicate membrane. The yolk is yel- 

 lowish-red, clouded, and marked with two 

 rows of small spots, globule-like, distinct at 

 one end, running together at the other. The 

 eggs in the central parts of the ovary are consi- 

 derably further advanced than those in the cir- 

 cumference. Through the transparent covering 

 of the egg the general form of the embryo can 

 be seen. 



Second stage. In this stage the young Cir- 

 riped resembles the fry of Cyclops or Daphnia 

 in its external characters. It is provided with 

 two long antennae and three pairs of feet (arms?) 

 placed along its ventral surface.* Each foot 

 of the first pair is single, and is furnished with 

 bristles at its free extremity. Each of the other 

 pairs is divided into two members, also tipped 

 with bristles. The posterior part of the body 

 is tapering, compressed, and slightly bifurcated 

 at its extremity, where it is beset with bristles. 

 No eyes could be seen in this stage, but Pro- 

 fessor Burmeister nevertheless conjectures that 

 they really do exist. The appearance of two 

 rows of small globules on the surface of the 

 body continues to present itself, but here they 

 are more numerous, although not larger. The 

 middle part of the body is clear and transparent. 



Third stage. Materials for the description 

 of this stage were obtained by Burmeister 

 from the examination of only one individual, 

 which was found attached to the frond of a 

 fucus hard by the bases of some adult indivi- 

 duals. The shell, in this the first stage of its 

 growth, is of leathery consistence, and formed 

 of one piece, placed dorsally. A fleshy protu- 

 berance serves as the peduncle. The organs by 

 which the young animal fixes itself are evi- 

 dently the long antennae situated near the 

 mouth. Behind these are placed the very large 

 eyes. Burmeister satisfied himself of the ex- 

 istence of a single transparent cornea, and saw 

 behind it a round black spot, but no lens. The 

 two eyes are very closely approximated by their 

 bases. Both the eyes and the brownish con- 

 tents of the alimentary canal can be distin- 

 guished through the translucent shell. In the 

 structure of the posterior part of the body there 

 is no great change from the former stage. Each 

 arm of the first pair is single, and consists of 

 three articulations, of which the basilar is the 

 greatest : the smallest and terminal one bears 

 four long stiff bristles. The arms of the follow- 

 ing pair are not single, but each is divided into 

 two small articulated processes. The little 

 globules of the two former stages are not dis- 

 cernible in this. 



* The circumstance of there being a smaller 

 number of arms in the young than in the adult, re- 

 minds us of the same being the case in several of 

 the Branchiopodous Crustacea; and the want of 

 the shell in young Cirripeds seems to point out a 

 closer analogy between them and Crustacea, than 

 between them and Mollusca, the young of which 

 are covered with shell in the egg. 



Fourth stage. This stage was observed 

 by Professor Burmeister in the Lepas ttnati- 

 J'era from the coasts of Chili. All the indi- 

 viduals examined were about three-fourths 

 of a line in length. Soon after the animal 

 fixes itself the old integuments are thrown 

 off. The eyes and the antennae are entirely 

 cast off along with these. After this process 

 had been completed, the space within the man- 

 tle was found to be filled with a granular pulta- 

 ceous mass, at first occupying the greater part 

 of the cavity of the shell, and covering all the 

 young animal. This appeared to M. Burmeis- 

 ter to be the same that is found in the pedicle 

 of the older animals, and to resemble closely 

 the matter contained within the cavities of the 

 shells of Coronulae and other Balanids. It is 

 by a sack-formed process of the mantle filled 

 with this yellowish matter that the peduncle is 

 first formed. At the time of the animal's fixing 

 itself the shell has no calcareous points, but in 

 the course of this stage it becomes firm and 

 gradually more and more solid. There are 

 now six pairs of feet, each of three articulations, 

 and terminated by bristles. A small tail of 

 two articulations also appears, the rudiments of 

 which, however, can be detected in the former 

 stage. In the fifth stage the process of deve- 

 lopment is completed. 



It must be admitted that the evidence in 

 favour of Mr. Thompson's opinions on this 

 subject is by no means conclusive. There is 

 still wanting a series of minute and careful ob- 

 servations on the first appearance and motions 

 of the embryo immediately after its exclusion 

 from the egg ; and nothing but the results of 

 such a series can settle the question as to whe- 

 ther there be a real metamorphosis or not. 



Mr. Gray's observations have led him to 

 conclude that no great changes of structure, 

 such as Mr. Thompson's views presuppose, 

 actually take place ; although, in examining the 

 mature egg of Balanus Cranchii, he found the 

 appearance of the embryo nearly the same as is 

 described by Burmeister as being that of the 

 Lepads in the second stage of development. 

 The egg of this Balanid Mr. Gray ascertained 

 to be one-fiftieth of an inch in length. He de- 

 scribes the inclosed animal as being of an ovate 

 form, tapering at one extremity, truncated and 

 ciliated at the other ; bearing a general resem- 

 blance to the adult animal, but furnished with 

 only three pairs of ciliated arms ; the base of 

 each arm being two-jointed. He found only 

 one lengthened process attached to the lower 

 pair of arms; but, connected with the two 

 upper pairs, two fusiform, thick, articulated 

 and ciliated processes, similar to those of the 

 anterior part of the perfect animal, but less 

 elongated. He saw no shelly covering.* 



We have not yet had proper opportunities of 

 devoting attention to this interesting subject so 

 far as observations on the living animals are 

 concerned ; but we have no doubt of its veiy 

 soon meeting with a clear and satisfactory elu- 

 cidation ; meanwhile we may remark that the 

 structure of the embryo within the mature egg 



115. 



Proceedings of Zool. Soc. Lond, 1833, pt. 



