692 



CIRRHOPODA. 



the shell ; which process is, at times, so much 

 elongated as to admit of the eggs hanging out 

 in groups from the brachial aperture, beyond 

 the extremities of the arms. Burmeister has 

 observed that, after the escape of the embryo, 

 the shells remain connected with the parent, 

 forming a loose net-work. This author seems 

 to regard these groups of eggs within the man- 

 tle, and the tissue in which they are imbedded, 

 as constituting the true ovary. In each of the 

 individuals of Anatifa striata which came under 

 his observation, he computed that there were 

 about 4000 eggs in the ovary. Mr. Thompson 

 calls these groups of ova conceptacles ; and 

 says that " each has a separate attachment at 

 the sides of the animal to the septum, which 

 divides the cavity occupied by the animal from 

 that of the pedicle."* The retention of their 

 ova, grouped in separate packets on the surface 

 of their bodies, after their expulsion from the 

 ovary, constitutes another point of resemblance 

 between the Cirripeds and Crustaceous animals. 



With regard to the anterior canal within the 

 ovary, little has yet been determined. We 

 have particularly examined it in Otion, and 

 find that, like its fellow of the dorsal aspect, it 

 leaves the ovary at its inferior edge, whence it 

 opens into a small cavity situated between the 

 intervalvular ligament and the lining membrane 

 of the visceral cavity. We have not succeeded 

 in discovering any orifice in the walls of this 

 cavity, although, from the results of some of 

 our experiments we think it probable that there 

 exists a small one just above the brachial slit. 

 If so, is it not likely that this is the passage in- 

 tended for conveying the fecundating liquor 

 from the orifice of the tubular process connected 

 with the male organs to the ovary ? When the 

 body is exserted through the brachial slit, the 

 point of the process can easily be brought into 

 contact with the outer surface of the cavity 

 above described. 



The development of the egg and the young 

 of the Cirripeds has recently become an object 

 of interesting inquiry in consequence of the 

 novel results announced by Mr. J. V. Thomp- 

 son in his " Zoological Researches," (1830, 

 4th Memoir.) This gentleman has published 

 an account of observations made on what he 

 believed to be the young of Balanids, from 

 which he concludes that, on their first exclusion 

 from the egg, they closely resemble some of 

 the branchiopodous Crustacea, that they pos- 

 sess the power of free locomotion through the 

 water by means of setiferous arms projecting 

 from within a bivalve shell, and that they 

 have very obvious pedunculated eyes. Minute 

 animals, bearing these characters, and having 

 some resemblance to species of the genus 

 Cypris, were placed by Mr. Thompson in a 

 glassful of sea-water. Soon after, on looking 

 for them, he could not find them in the water, 

 but he found in their room several very young 

 balanids, which, from the appearance they pre- 

 sented, he concluded to be really the same 

 animals that he had originally placed in the 

 water, changed by metamorphosis. Mr. Thomp- 



* Phil. Trans. 1835, 356. 



son has not seen the change actually going on, 

 but he has satisfied himself that what he re- 

 gards as the free-moving embryo fixes itself by 

 a spot on its dorsal aspect between the two 

 shells, which spot can be seen during its free 

 state. When fixed, the base of adherence ap- 

 pears to be broad like that of an Actinia : from 

 this it rises in a conical form, truncated. The 

 flat sides of this cone are coated with six shelly 

 plates, so arranged as to leave a large space in 

 the middle uncovered. This space is closed 

 by the old shells of the embryo state, which 

 are made to move up and down as the opercule 

 does in the adult animal, admitting of the 

 egress and ingress of the arms at the animal's 

 pleasure. Through this shell two large black 

 spots like eyes can be distinguished. Mr. 

 Thompson found in the young of the Balanids, 

 six pairs of arms, cleft ; each arm with two ar- 

 ticulations. The first casting of the shell, after 

 the animal has fixed itself, is followed by an 

 increase in the number of articulations in each 

 arm ; and this number is further added to at 

 every succeeding shell-casting. Even the old 

 full-grown animals, according to Mr. Thomp- 

 son, cast their shells. 



Very recently Mr. Thompson has made a 

 still more satisfactory series of observations on 

 the development of some of the Lepads, of the 

 genera Cineras, Otion, and Lepas. These he 

 obtained from the bottoms of vessels in the 

 harbour of Cork. They hatched eggs in large 

 numbers, and afforded him the means of ascer- 

 taining, entirely to his own satisfaction, that, at 

 its first exclusion from the egg, the Lepad, like 

 the Balanid, is a natatory crab. He found a 

 considerable difference between the larva of 

 the two classes. The newly-discovered one of 

 the Lepads he describes as " a tailed monocu- 

 lus, with three pairs of members, the most an- 

 terior of which are simple, the others bifid, 

 having its back covered by an ample shield, 

 terminating anteriorly in two extended horns, 

 and posteriorly in a simple elongated spinous 

 process." 



The general appearance of this larva is not 

 unlike that of the Argulus armiger of La- 

 treille.* 



Very recently Messrs. Audouin,f Wagner,^ 

 and Burmeister, have corroborated the state- 

 ments and supported the views of Mr. Thomp- 

 son. Professor Burmeister has detailed the 

 results of his observations with great minute- 

 ness. It appears that they were made chiefly 

 on individuals of Anatifa striata, procured in 

 the North Atlantic Ocean, and preserved in 

 spirits ; partly also on Lepas anserifera. (Linn.) 

 The results of these observations have led Pro- 

 fessor B. to divide the development of the Cir- 

 ripeds into five stages or periods. The ( /iVs of 

 these is the state of egg ; the second is that of 



* Phil. Trans. 1835, pt. ii. 355. " Discovery of 

 the Metamorphosis in the second type of the Cirri- 

 peds," &c. 



f Ann. des Sc. Nat. n. s. iii. 31. 



j Miiller's Archiv, No. 5, 1834, and Beitrage zur 

 verglrich. phys. des Blutes. Leipzig, 1833. 



Beitrage zur Naturgcsch. dcr Rankenfusser. 

 Berlin, 1834. 



