506 Miscellaneous. 



tory vesicles were shrunken into longish sacs, closely surrounding 

 the otoliths. In somewhat older animals there was no trace of the 

 organs of sense, although they had not lost their sensibility to light. 



One of the larvae lived for a month after its adhesion ; but from 

 the lapse of a day before its death was noticed, the soft parts had be- 

 come greatly decomposed. The older bristles of the free larva 

 appeared to be still present, as also the plumose bristles of the ante- 

 rior margin. Besides these, there was on each side, about in the 

 middle between the median line and the origin of the great bristles 

 of the fourth pair, a straight smooth bristle, 0*2 mill, in length, 

 projecting obliquely backward, little thicker than the strong posterior 

 setse, but with a much stronger outline. 



It is remarkable that in two years the author has repeatedly 

 captured free-swimming larvse which had evidently advanced further 

 in their development than the oldest of those which had already fixed 

 themselves. They were all destitute of the transversely oval plate, 

 and of every trace of organs of sense ; the plumose setae of the ante- 

 rior margin were also wanting, as were, more or less entirely, the older 

 bristles. Of the more delicate bent bristles, some were usually still 

 present, and these appeared to be unabbreviated, so that the missing 

 ones had probably been lost by shedding. The stronger bristles, on 

 the contrary, are gradually absorbed at the base ; at least this is the 

 case with the fourth pair : these were repeatedly met with of about 

 half their proper length ; the stalk, with its fusiform dilatation, had 

 disappeared, whilst the apex remained readily recognizable by its 

 peculiar curvature and denticulation. In a still older animal about 

 a fifth of the length was still present, so that it no longer extended 

 beyond the margin of the shell. This animal (the oldest examined 

 by the author) had lost all the older setse except this small residue. 

 On the other hand, the two straight smooth bristles, which, in the 

 oldest attached animals, scarcely began to protrude from the shell, 

 had attained a length of double the diameter of the shell, and being 

 inserted into thick muscular sheaths were strongly and rapidly 

 moved by the animal, sometimes spread out horizontally, sometimes 

 again crossed backwards. 



During this complete change of the setae the soft parts had under- 

 gone no essential alterations. The roundish stomach, reaching from 

 the front to the middle of the longitudinal diameter, still showed the 

 two dark spots of the young larva, which remind one of the similar 

 spots in the larvae of some Bryozoa. From the back of the stomach 

 sprang the intestine, which bends under the margin of the stomach 

 to the right, and then forwards, terminating about the middle of its 

 right side. The oesophagus goes from the front of the stomach 

 straight forward halfway to the front of the shell, and then bends 

 downward, so that the mouth lies close to the stomach. The arms, 

 especially the two middle pairs, had become longer and slenderer, 

 and the knob between the anterior pair had diminished in size. No 

 vessels or pulsating heart were recognized. — Wiegmann^ s Archiv, 1861. 

 p. 53. 



