ASTEROIDEA 



spine sheath ruptures leaving the spine-tip bare and part of the sheath attached to the 

 opposite body wall. 



As the 5-9 eggs of each "basket" develop, the first intercostal membrane becomes 

 more and more concave. The young usually have their ventral surface against the sides 

 of this basin-like hollow, but not invariably. There are usually 2 or 3 which are de- 

 veloped much further than the rest. Those shown in the enlarged photograph are 

 probably nearly ready to escape. Beneath such young, crowded against the pouch wall, 

 there may be several very immature ones, or even eggs. 



In a sample brood chamber of the large 13-armed specimen, St. 123, were 8 young in 

 2 stages : (i) three in the youngest stage as described below, rays 12, 13, 14 ; (2) five with 

 13 rays in stage 4. The next pouch, B, has 2 eggs; three young in the first stage (one 

 with 1 1 rays, two with 13 rays) ; three (with 13 rays) in stage 4. Pouch C, same specimen, 

 had a cluster of 6 eggs and three 13 -rayed young in stage i. 



This is the first instance of brooding reported for the Brisingidae and is noteworthy 

 for the position of the nursery as well as for the details of adaptation. Especially extra- 

 ordifiary are the permafient spine bridges across the dorsal side of the chamber. 



Developmental stages. The eggs found in brood pouches are subspherical, some- 

 times slightly flattened on one side, 1-5 mm. in diameter. One ellipsoid 2 mm. by 

 1-4 mm. was found. 



Stage I. In the earliest stage encountered (Fig. G, 4) the total diameter is 2-5 mm. 

 The disk is low hemispherical and the rays from above are scarcely more than buds 

 0-3-0-4 mm. long. The disk is beset with widely spaced spine buds. The circle of the 

 actinostome occupies most of the actinal surface. The nerve, terminal organ, and 3 or 

 sometimes 4 pairs of tube-feet have appeared, and swellings of the end of ray on either 

 side of the terminal tentacle indicate the first terminal spinelets. The oral angle is 

 sketched in but there are no calcareous plates. Distance from oral angle to tip of ray, 

 0.65-0-75 mm. A specimen prepared in sodium hypochlorite has the beginnings of the 

 following plates: abactinal of disk (46-J); 4 pairs of ambulacrals, 2 of adambulacrals 

 (no spinelets); terminal (2 spinelets). All these are in a very embryonic state. There is 

 no trace of pedicellariae. 



Stage 2 (PI. XVI, fig. 9). Diameter about 3-5 mm. The chief advance is the appearance 

 of numerous pedicellariae on the conspicuous sheath in which the 4 or 5 terminal 

 spinelets are immersed. The rays are relatively longer to the still strongly convex disk; 

 diskspinelets longer ; tiny mouth pore ; 2 adambulacral spines ; rudimental mouth-plates ; 

 4 pairs of tube-feet. Distance from actinostome to end of ray, i mm. (i example from 



type)- 



Stage 3. Diameter 4-25 mm. Rays slightly longer, but no abactinal spinelets; disk 

 strongly convex with subcircular embryonic plates, their spinelets slightly longer than 

 in 2 ; terminal ruff of pedicellariae larger ; 6 terminal spinelets, 4 pairs of tube-feet with 

 rudiments of fifth pair on some rays, the proximal 3 pairs relatively slightly larger than 

 in 2, and with strong sucking disks ; 3 adambulacral spinelets on each side of furrow ; the 

 rudiment of a lateral oral spine to each mouth-plate (as in stage 2, PI. XVI, fig. 9) but 



