Miscellaneous. 423 



than those at any other point of the larva. When the gastrula 

 is swimming these long cilia are directed forwards, now and then 

 sway to and fro slightly, bnt never aid in propelling or turning 

 the larva, apparently being inactive except that occasionally they 

 eeem to act as sensory cilia. In some few cases this area with the 

 long cilia was somewhat thicker than the neighbouring ectoderm. 

 This thickening of the ectoderm and greater length of cilia over this 

 thickened area was very marked in many Strongi/locentrotus-gus- 

 trulse, and it was always easily recognizable in Ophiothrisv, and was 

 well marked in Moira. Nothing of the kind was observed in the 

 few starfish-gastruke I was able to get. That we have here to do 

 with a differentiation peculiar to this part of the larva only, and 

 that it is to some extent comparable to the region of the praeoral 

 tuft of cilia of other larvae, is shown by the fact that it is marked 

 some time before the larva escapes from the membrane, and that 

 it exists long before there is the slightest indication of the posterior 

 and the unmistakable anterior ridge of the ciliated band of the 

 future Pluteus. And that it is not an optical delusion due to a 

 difference in the rapidity and manner of vibration of the cilia in 

 different parts of the larva is proven by specimens killed on the slide 

 with osmic acid or other hardening fluid. How much importance can 

 be attached to this fact will be discussed in a later paper. In passing 

 I would, however, here point out that it is possible to explain the 

 praeoral band of cilia of Bipinnaria as a modified form of this group 

 of long cilia, and that in those forms where we have but one band 

 of cilia, these long cilia of the gastrula have merged into the ante- 

 rior ridge of cilia, which then united with the postoral ring. The 

 body-cavity and water-vascular system of Mellita is derived 

 from a two-horned diverticulum of the enteron, just as inStronyylo- 

 centrotus. In Moira the process of segmentation, which is regular 

 only up to eight blastomeres, leads to a blastosphere, this to a 

 bilaterally symmetrical gastrula, which gradually develops into a 

 nine-armed Pluteus, the posterior unpaired arm arising soon after 

 the two ventral ones. No polar globules were seen. The body- 

 cavity and water-vascular system arise as they do in Mellita. A 

 phenomenon observed one da)^ while fertilizing some immature eggs 

 of Moira deserves mention here. The immature eggs have a clear 

 distinctly visible nucleus and a number of clear spaces of varying 

 sizes. Some of these eggs were mixed with active spermatozoa, 

 and in a few moments after the spermatozoa had been added quite 

 a number of pseudopodia were thrust through the egg-membrane, 

 which, after having felt about a short time, again slowly withdrew 

 themselves. The eggs did not undergo segmentation, and some 

 hours later disintegrated. Want of time did not permit me to 

 experiment in this direction. 



The small opaque eggs of OpMothrix always threw off two polar 

 globules after being mixed with the male fluid. The first two 

 planes of segmentation are meridional, the third is equatorial. 

 The eight blastomeres are equal in size. As in the cases mentioned 

 above, so here segmentation begins to be irregular. In the cases 

 that came under my observation the segmentation of Ophiophragma 

 was regular till four blastomeres had been formed. These eggs 



