2l8 WILSON. [Vol. IV. 



I hesitate to suggest that two such experienced observers as 

 Hatschek and Fraipont can have fallen into error on this point, 

 yet it is a singular fact that neither of them figures or refers to 

 the conspicuous prae-anal gland-cells, while both describe a large 

 mesoblast-cell in exactly the same position, but lying below the 

 surface. Each gives a single figure of the "primary mesoblasts" 

 in cross-section, lying in the cleavage-cavity. But Hatschek 

 gives also, in the same series of figures, exceedingly definite 

 representations of "die fotalen Langskanalen," which, as Meyer 

 and Fraipont have shown, and as I have convinced myself from 

 the study of many series of sections, have no existence in 

 nature. Fraipont's figure is scarcely more satisfactory. The 

 minute nuclei and clear protoplasm of his figure have no resem- 

 blance to the large, conspicuous nuclei and granular protoplasm 

 of teloblasts ; they at once suggest the small nuclei and vacu- 

 olated cell-body of the "anal gland-cells." A closely similar 

 view might easily be had of a rather thick, slightly oblique 

 section, the "gland-cells" being tangentially cut, and appearing 

 to lie inside the ectoblast on account of the sharp curvature of 

 the surface where they lie. And in view of these facts I venture 

 to suggest the desirability of a re-examination of the mesoblast- 

 bands in the European species of Polygordms. 



The non-existence of the teloblasts in later stages, which is 

 apparently the rule among the Polychaeta and {.?) Archiannelids, 

 by no means, however, affords any presumption that they are 

 not present in earlier stages. The case of Nereis shows that 

 it will not be safe to assume the absence of teloblasts without 

 following the development, cell by cell, from the very beginning, 

 and that wherever it is possible to make such a detailed study, 

 we may pretty confidently expect to find teloblasts. There is, 

 I believe, every reason to believe that in Hydroides, for example, 

 the two groups of mesoblast-cells take origin in two cells, though 

 they may appear at so early a period and differ so little in 

 appearance from the adjacent cells as to elude any but the most 

 searching examination. And it does not seem very rash to 

 predict that the secondary mesoblast-bands, even of Lopado- 

 rhynchus, will yet be shown to arise by teloblastic development. 



Marine Biological Laboratory, Wood's Holl, Mass., 

 September, 1890. 



