116 BULLETIN OF THE 



he has interpreted as water-tubes, and I am led to regard it as admitting 

 another interpretation from his. It shows that what he regards as mouth 

 may be in reaUty the anus. I am not wholly settled in mind, however, 

 in this conviction, especially if the two transparent bodies (v) are, as he 

 interprets them, water-tubes, the right and left vaso-peritoneal vesicles. 

 Their position would lead to the belief that Metschnikoff's interpreta- 

 tion is correct, for in all Echinoderms these bodies are found one on each 

 side of the plutean or brachiolarian mouth. Subsequent larvae, which 

 are here figured, show that the provisional plutean appendages are not 

 necessarily first formed at the anal pole, as these are situated in the larva 

 he figures. 



Mouth, (Esophagus. — The mouth (or) of Araphiura is formed by invag- 

 ination, I was in doubt when I wrote my preliminary account of the 

 development of Ophiopholis whether the primitive gastrula opening be- 

 came mouth or anus of the pluteus. My figures* seem to indicate that 

 the gastrula mouth becomes the plutean mouth ; and if that is true, Ophi- 

 opholis is certainly exceptional. I find the same difficulty in the study of 

 the development of Amphiura, although it seems as if the general law * 

 of Echinoderm development ought to hold here as in Strongylocentrotus 

 and others. In a bisymmetrical larva of Amphiura (PI, II, Fig. 4) we have 

 oesophagus, stomach, and intestine well developed. If there is in this 



♦ Op. cit., PI. L The law referred to is that the first opening, blastopore, is the 

 future anus, and a second opening is found to develop into the pluteus mouth. This 

 law has been found to hold in several genera of Echinoids, but has not been supported 

 by observations of the Ophiurans. The supposition has been that in Ophiurans the 

 law is the same as in Echinoids. Observations are now wanting to prove that such 

 is the case. In my paper on the development of Ophiopholis it was not possible for 

 me to prove that the gastrula mouth, blastopore, becomes the vent of the pluteus. 

 The lettering gni (PI, IV., Bull. Mus. Comp. Zobl., "Vol. XII. No. 4) of the gastrulae 

 of Echinarachnius is a typogi-aphical error, as a reference to my text will show. In 

 some other Echinoids the blastopore becomes the vent of the pluteus, according to 

 most authorities. I have not observed the fate of the blastopore in Echinarachnius, 

 and this erroneous lettering might imply that I was sure that the blastopore becomes 

 the pluteus mouth. The candid reader of my text {pp, 128, 129) will I hope acquit 

 me of holding that the blastopore becomes the pluteus mouth in Echinarachnius, Of 

 the origin of the mouth of the pluteus it is said (p. 128) : " The walls of this infold- 

 ing" (second invagination) "break away and form the future anus {v) of the stages 

 immediately following the gastrula, and probably the mouth of the pluteus," Of the 

 fate of the blastopore in Echinarachnius I have no observations, and "nothing to 

 show that there is any difference in this genus from what is recorded in Strongylo- 

 centrotus and other Echinoids " (p. 129), 



