THE DEVELOPMENT OP ASTERINA GIBBOSA. 235 



small cubical cells ; the ectoderm is made up of exceedingly 

 long and narrow cells bearing flagella, and the wall of the 

 hydrocoele of similar cells, but I could not make out any 

 flagella there. Fig. 144 is taken from the posterior end of the 

 animal on the right side ; the form of the ectoderm cells is 

 well seen, and one observes occasional goblet cells (gob.) 

 amongst them. The section goes through a peculiar patch of 

 peritoneum, where the cells are actively engaged in budding 

 off the amoebocytes which float in the coelom. So far as I can 

 make out, however, no cells are budded off at this stage into 

 the blastocoele (i. e. the space between the ectoderm and the 

 coelomic wall), and the mesenchyme cells are as yet entirely 

 undifferentiated. The characters of gut cells are shown in 

 PI. XIX, fig. 126. Although this is taken from a larva in which 

 the metamorphosis has commenced, yet the characters of these 

 cells do not vary till the very close of the metamorphosis. 

 They have the same general form as the ectoderm cells, but 

 the bases of the latter are often contracted, and leave chinks 

 between them, whereas the endoderm cells are closely apposed 

 to one another. Fig. 126 also shows another point of interest: 

 here and there a small round amoebocyte may be seen applied 

 to the basal end of the gut cells, and one discovers amongst 

 the latter also one or two rounded cells, thus suggesting that 

 these amoebocytes may be able to pass between the gut cells 

 like the lymph cells in the Vertebrate intestine. 



Plate XX, figs. 133 — 135, are three sections through the larval 

 organ which have already been alluded to. It is to be noted 

 that in this stage the adhesive disc has short cilia, just as See- 

 liger (18) has described for the adhesive disc of Antedon. Where 

 I have put " nerv. larv." a thin strand of pale fibrous matter is 

 observable with the highest powers. This is the only trace I 

 can discover of a larval nervous system, and I am not perfectly 

 satisfied about it, since it does not take the yellowish-brown 

 tone with osmic acid so characteristic of the adult nervous 

 system. Should my interpretation of it be correct, the larval 

 nervous system would consist of a layer of " Punktsubstanz " 

 underlying the larval organ. 



