No. 2.] THE MllSOBLASr-BANDS LV ANNELIDS. 217 



abundant at Newport. In the very large series of larvas in my 

 possession all stages are represented from the adult condition ^ 

 down to the youngest described by Hatschek and Fraipont. 

 The species is closely similar to P. neapolitajtiim as described 

 by Fraipont. An examination of the mesoblast-bands in these 

 larvas showed, to my extreme surprise, that no teloblasts of any 

 kind are /^resent, even in the youngest stages. The mesoblast- 

 bands end behind, as in Hydroidcs, in a group of two or three 

 cells, which are somewhat larger than those in front, it is true, 

 but have none of the characteristics of teloblasts. Only in a 

 single case have I found at the tip of the band a cell distinctly 

 larger than the others, and this was on one side only. Is this 

 absence of the pole-cells peculiar to the American species of 

 Polygordins f Possibly ; yet there is a fact that forces me to 

 suspect the possibility of error on the part of Hatschek and 

 Fraipont, improbable as such a suspicion may appear. If the 

 germ-bands of a young larva be viewed en face from the ventral 

 side in suitably prepared specimens, a very clear picture of the 

 germ-bands will be seen, closely similar to that represented 

 in Hatschek's Fig. 57. At the tip of each germ-band is a large, 

 rounded, clear cell, meeting its fellow in the median line just 

 in front of the anus, and to all appearances a " primary meso- 

 blast." For such I at first mistook these cells, but, to my great 

 surprise, sections in the various planes all agreed in showing 

 that they formed part of the ectoblast, lay at the surface of the 

 body, and had no connection whatever with the mesoblast- 

 bands, though the latter end just below them. These cells 

 are clear, vacuolated, with minute nuclei, and are undoubtedly 

 homologous with the anal vesicles or anal glands of other 

 annelid trochophores ; though as far as I am aware they are 

 here described for the first time. They have no connection 

 with the paratroch. 



1 I have repeatedly observed the sudden metamorphosis of the last larval stage into 

 the adult, which has been briefly mentioned by Kleinenberg. The cells of both the 

 prototroch and paratroch are suddenly thrown off, and continue to swim for some 

 time after their complete separation from the body of the young worm. The proto- 

 trochal cells are often thrown off, over the head, in the form of a girdle, which in 

 some cases — I have observed it at least four or live times — is swallowed and 

 digested by the animal. This recalls the curious habit of Actinotrocha, which at its 

 metamorphosis throws off and swallows the greater part of the prse-oral lobe (Cald- 

 well). This metamorphosis certainly throws an interesting light on the origin 

 of such a mode of development as that of Pilidium. 



