DEVELOPMENT OF ANTEDON (COMATULA, LAMK.) IIOSACEUS. 753 



Brachial of one of the Aims acts as an axillary segment, bearing two small 

 Arms. — Magnified 3i diameters. 



Fig. 9. Calyx and Basal portion of Arms of a specimen which seems, like the last, to 

 have lost one of its Eays at the junction of the First and Second lladials, 

 the Eay and Arms having been reproduced on a smaller scale. — Magnified 

 3i diameters. 



Fig. 10. Basal portion of Arms with the soft parts removed from their ventral surface, 

 so as to show the disposition of the Muscles ; r'^, Third Radial, with its pair 

 of Muscles on either side connecting it with ir' the First Brachial ; between 

 this aiid the Second Brachial, br, there is only ligamentous union ; the next 

 pair of muscles connects the Second with the Thii-d Brachial, ir^ ; between 

 the Third and the Fourth Brachial there is a syzygy, 517 ; and beyond this 

 the muscles connect every segment with that wliich succeeds it, except where 

 a syzygy intervenes. The small muscles connecting the segments of the Pm- 

 nules are also shown. — Magnified 15 diameters. 



Fig. 11. Vertical Lonsritudinal Section of an Arm taken near its base, to show the 

 arrangement of its Muscles, m, m, and its Ligaments, I, I, and the interruption 

 of these at the syzygy, s(/. — Magnified 15 diameters. (See also Plate XLIII. 

 fig. C.) 



PLATE XXXIX. 



Fig. 1. Group of Pentacrinoid larvae of Antedon rosaceiis in different stages : — a, showing 

 the Basals, b, b, the circlet of First Eadials, r\ r\ already complete, the rudi- 

 mentary Second and Third Eadials supported by this, and the circlet of Orals, 

 0, 0, alternating with these and resting on the First Eadials ; B, showing the 

 incipient development of the Arms from the extremities of the Third Eadials, 

 the relative positions of the other parts being but little changed, and the Dorsal 

 Cirrhi not having yet made their appearance (see Plate XLI. fig. 1 for a repre- 

 sentation of the skeleton in this stage on a larger scale); c, showing the 

 fm-ther development of the Arms, the incipient opening-out of the Calyx 

 occasioned by the increased development of the First Eadials, and the first 

 appearance of the Dorsal Cirrhi ; D, showing the first appearance of Pinnules 

 at the extremities of the Arms, the fm-ther opening-out of the Calyx (bringing 

 the vent into view^), and the formation of the first whorl of Dorsal Cirrhi 

 (see Plate XL.) ; E, showing the Pentacrinoid ready to assume its free condi- 

 tion, two rows of Dorsal Cirrhi being now completed, the Arms being con- 

 siderably elongated by the addition of new segments, and several pairs of 

 Pinnules bcinsr formed at their extremities. — Magnified 1.5 diameters. 



Fig. 2. Skeleton of early Pentacrinoid larva, from a dried specimen, showing the mode in 

 which the Calyx can be (in that stage) completely closed in by the folding 

 together of the Orals, 0, 0. — Magnified 70 diameters. 



5 k2 > 



