EXPLANATION OF THE PLATES. 



(5) 



opening of the mouth. The tube leading from the 

 water-pore (b) (dorsal pore) to the water-tube («>'), 

 is quite distinctly seen. 

 Fig. 28. The same larva as Fig. 27, seen from below; 

 the intestine as in Fig. 26, is thrown to one side 

 of the axis of the larva. The water-tubes extend 

 also along the sides of the stomach towards the anal 

 extremity; the sinuosity of the anal ciliary chord in- 

 dicates the position of the future anus. 



Plates III. — VIII. Embryology of Astera- 



CANTHION PALLIDTJS Ag. 



PLATE III. 



Owing to the transparency of these larvae, it is not easy 

 to ascertain whether they are seen with the mouth 

 downwards or upwards, unless we ascertain the po- 

 sition of the madreporic body. In all these figures, 

 whenever the water-tube w< is on the left of the 

 figure, the mouth is turned upwards. 



Fig. 1. The youngest larva of this species, seen from 

 the mouth side, corresponding to PI. LI. Fig. 20 ; a 

 comparison of these two figures will show the great 

 difference between the larvse of these two species of 

 Starfishes. In the former, the chords of vibratile cilia 

 appear much earlier, and the oral plastron is well 

 defined ; while, in the other species, it is not before 

 it has reached the condition of PI. II. Fig. 26, that 

 the oral plastron is as well developed. 



Figs. 2-10. • Brachina stage. 



Fig. 2. A larva seen from the left profile, corresponds to 

 the stage of PI. II. Fig. 27 of A. berylinus ; with 

 the exception of the size of the water-tubes, the larva 

 of this species is much stouter, shorter, and the anal 

 portion is the most prominent, while the larva of the 

 A. berylinus is quite slender and elongated. 



Fig. 3. The same larva as Fig. 2, seen from the dorsal 

 side. 



Fig. 4. A more advanced larva, seen from the dorsal 

 side; the undulations of the ciliary chord indicate the 

 future arms, the water-tubes extend beyond the mouth, 

 and have already begun to bend towards each other. 



Fig. 5. The same larva seen from the left profile, to 

 show the bent attitude frequently assumed by the 

 larva when disturbed. 



Fig. 6. This larva, seen from the mouth side, is more 

 'developed than any raised by artificial fecundation 

 from the eggs of A. berylinus. The water-tubes have 



greatly increased in diameter; they have united be- 

 yond the mouth, and extend on each side of the 

 stomach so as almost to meet, but without uniting. 

 The mere indentations of the previously figured larvse 

 correspond to accumulations of pigment cells, and to 

 the thickening of the vibratile chord, accompanied by 

 the formation of rudimentary lobes, which indicate 

 plainly the position of the median arms (e'), the 

 dorsal anal (e")> the ventral anal (e'")j and dorsal oral 

 arms (e""). The greatest accumulation of pigment 

 cells, and the thickening of the vibratile chord, is found 

 at the rudimentary median arms (e'). The anal ven- 

 tral pair of arms (e'") is especially well marked. 



Fig. 7. The preceding figure seen in profile, the mouth 

 to the right, shows the great development which the 

 oral position of the water-tube has taken; also the 

 mode of formation of the oral ventral pair of arms (e B ), 

 as well as the first sign of the odd brachiolar ap- 

 pendage {f a). 



Fig. 8. Larva seen from the dorsal side. The arms have 

 increased greatly in size since the stage represented 

 in Fig. 6. The oral portion of the water-tube has 

 become very pointed ; it extends into the odd oral 

 arm (e 6 ), which has also elongated, and stands out 

 prominently beyond the oral plastron. 



Fig. 9. The same figure seen in profile, with the mouth 

 downward. The vibratile chord is a deeply undulat- 

 ing line, following the edge of the arms, which extend 

 beyond the general outline. The water-tube, it will 

 be seen, forks also at the_ oral extremity; one branch 

 extending into the odd arm (e 6 ), the other toward 

 the" angle made by the base of this arm and the 

 pair of oral ventral arms (e s ). The great increase 

 in size of this odd arm will be seen when compared 

 to Fig. 7 of this plate. 



Fig. 10. Larva seen from the mouth side. Thus far the 

 arms had altered but little the character of the outline 

 of the larva. In this figure, however, some of them are 

 sufficiently developed to be capable of extensive motion. 

 The median arms (e') especially are far in advance 

 of the others. All the anal arms develope so as to 

 become more slender at first, and assume their true 

 character sooner than the oral arms, which, during 

 the early stages, are always more heavy, and take 

 their final shape later than the anal arms. At the 

 angle, where the oral ventral arms and the odd 

 * arm come together, at the base of the oral arms, 

 slight swellings are formed (/), which are the first 

 trace of the pair of brachiolar arms (//), the 

 odd brachiolar arm being only seen in the profile 



