436 Prof. Muller on the Larval State and the Metamorphosis 



that part of the Pluteus where the mouth was situated. This 

 region now appears as if forcibly drawn obhquely upwards, and 

 no further trace of the mouth of the larva is seen. But instead 

 of the former lateral mouth of the Pluteus, there now appears a 

 central mouth for the Echinoderm. 



I have not been able to decide whether the mouth of the larva 

 is transformed into the mouth of the Ophiura, or whether the 

 latter is of perfectly independent origin and the former disap- 

 pears. In the true Echinida, as in Echinasterj that spot in the 

 newly-formed Echinoderm, at which the mouth is subsequently 

 situated, is still perfectly closed, even when the first tentacles are 

 formed. The mouth of the young Ophiura is at first round and 

 totally dissimilar to the mouth of the larva ; it gradually assumes 

 a stellate form. 



In the Echinida, where, as we shall hereafter see, four sides 

 can be distinguished in the larva, the formation of the mouth of 

 the Echinus is always independent of the mouth of the larva ; 

 for none of the poles of the young Echinus formed in the larva 

 correspond to that side of the larva in which the mouth of the 

 larva occurs. 



In its present condition the newly -formed star-fish is always 

 smaller than the remains of the Pluteus, but the more the star- 

 fish grows, the more do the appendages and the azygous apex of the 

 Pluteus appear as mere appendages of the star-fish. The azygous 

 summit of the Pluteus, its two long lateral arms, and one of the 

 two lower arms remain longest, but on the growth of the star-fish 

 these at last also disappear. The stomach is the only structure 

 in the new being which is completely received from the Pluteus, 



The tentacles or feet of the young star-fish are also formed be- 

 fore the arms of the Pluteus disappear. At first there are only ten 

 of them, which inclose the disc itself in a crown. Before the 

 loss of any of the arms, two foramina are formed in the disc, 

 from which the animal exserts the tentacles. At this period it 

 still lives in the sea as before, but when it lies on the bottom of 

 a vessel, it gropes about with the tentacles. The tentacles or 

 little feet are covered with small knots, as in the Ophiura. In 

 this state the animals move exactly as formerly by ciliary action, 

 and we very frequently see the circular rotation in the plane of 

 the longest or lateral arm of the Pluteus. So far we are un- 

 able to guess from the form of the animal, whether an Asterias 

 or an Ophiura will form from the Pluteus ; its remarkable difi'er- 

 ence from the larva of the Asterias of Sars indicates something 

 distinct, and in fact the characters of the Ophiura soon show 

 themselves. Shortly before the time when the last traces of 

 the Pluteus disappear, we see that the arms of the star-fish 

 are deposited by the disc and as it were articulated. But this 



