the Develojjment of Phyllodoce maculata. 107 



which is simply blocked out, occupying little more than two- 

 thirds of the space in front of the vibratile ring and of the 

 large shield extending behind it: when seen in profile (fig. 47, 

 upper figure) , the cavity is somewhat retort-shaped, and occu- 

 pies mainly the dorsal portion of the embryo." In the much 

 younger animals examined by me, the large aperture behind 

 the ciliated ring is very conspicuous, and assumes various 

 shapes in regard to contraction and dilatation. From the 

 posterior border of this opening a series of short cilia proceed 

 towards the tip of the body; but, as their distribution is 

 limited, they are not very evident in all ^^ews. No aperture 

 Avas seen at the posterior termination of the body, neither was 

 any made out at the anterior ciliated tuft. This large aper- 

 tiu-e behind the ciliated ring (supposed by Prof. Sars to be the 

 anus) would therefore appear to be the mouth — an interpreta- 

 tion in accordance with what is found in other young Annelids, 

 such as Polynoe. The ciliated ring is a very common arrange- 

 ment in the Annelidan young, the homologue thereof appear- 

 ing even in the Xemerteans, for instance, in the temporary 

 tufts of long cilia on the snout (in front of the mouth) of the 

 developing Cephalothrix JiUformis. The Xemertean young- 

 are ciliated all over — a distinction between them and the Anne- 

 lids, however, that has exceptions. A. Krohn and A. Schnei- 

 der*, for example, describe a young bristled form from the 

 Mediterranean, entirely covered with cilia in the early stage. 



EXPLANATION OF PLATE VI. 



JFT^. 1. Newly deposited ovum of Phyllodoce macuJata, Johnst., surrounded 



bv spermatozoa, X 350 diameters. 

 Fig, 2. Spermatozoa of the same species, drawn under a power of 700 



diameters. 

 Fig. 3. The ovum, with the yelk separated into two divisions, X 350 diams. 

 Fig. 4. The same, separated into four divisions, x 350 diams. 

 FS,g. 5, Rounded embryo shortly after the appearance of the cilia, X 



350 diams. 

 Fig. 6. Embryo somewhat older, and having two eyes, and longer oral 



and lateral tufts of cilia (the latter of course arising from the 



ciliated ring under pressure), X 350 diams. 

 Fig. 7. A younger embrt'O than the foregoing, viewed from the anterior 



end, and slightly compressed. The digestive chamber is clearly 



mapped out. 

 Fig. 8. Embryo about five days old, seen from above, almost in its normal 



state as regards pressure, x 350 diams. 

 Fig. 9. The same, \-iewed from the anterior end, uncompressed, X 350 



diams. 

 Fig. 10. Elements of compressed and disintegrated animal, X about 



700 diams. 



• Archiv fiir Anat. 1867. p. 498, Taf. 13. I 1 .t 2. 



