NEW RESEARCHES 85 



tion between them as to size attention must be given to their accompanying 

 signs of enlargement. 



The anatomical processes by which the foregoing changes in the larvae 

 of Comactinia (Actinometra) are accomplished, as contrasted with those in 

 Antedon, are as follows : 



Observation by transmitted light of two specimens in the early prebrachial 

 stage (PL B, figs. 1, 2b), confirmed by dissection of another, shows that the 

 alimentary canal consists of a mouth, surrounded by a narrow lip from which 

 the oral tentacles spring; a short, broad, funnel-shaped oesophagus; a hori- 

 zontal portion distended transversely resembling the human stomach, into the 

 larger end of which the oesophagus opens; and a slender intestine ending 

 blindly which originates from the smaller left end of the stomach, makes a half 

 twist and coils dextrally around it. This simple alimentary system is loosely 

 suspended in the coelom by threads and lamellae of connective tissue, and is in 

 contact with the inner wall of the cup only at the mouth and the posterior end 1 . 

 The intestine in its development has coiled dextrally around the stomach, then 

 turned obliquely upward towards the posterior interray; the upward turning 

 having started near the middle of the anterior border of the right-posterior 

 basal, and ending in this stage with the formation of the anus slightly to the 

 right of the posterior interradial plane, on a level with the distal margins of 

 the incipient radials. The upward bend of the intestine, which appears) in the 

 posterior interray of Antedon shortly after the "Antedon stage " is reached, 

 in this form does not come to lie in the posterior interradius until a very much 

 later stage of development. Dissection at the stage of figure 9 shows the 

 upward turn still to the right of the posterior interray. As the cup expands 

 laterally and vertically the intestine also expands, but growing more rapidly 

 ihan the calyx soon fills the body cavity. The radianal, formed previous to and 

 just below the anus, is parallel to the intestine at that point, and evidently very 

 firmly attached to it, 1 as shown by its subsequent migration. The upward 

 growth of the cup and the concomitant dextral growth of the intestine carry 

 the radianal and the anus upward and into the plane of the posterior inter- 

 radius ; which by reason of the retirement of the oral distalward is the path of 

 least resistance. When the portion of the intestine to which the radianal is 

 attached comes to lie in a vertical position along the plane of the posterior 

 interray the radianal is completely withdrawn from the radial circlet, and rests 

 equally upon the truncated, disto-lateral margins of the posterior radials (PI. B, 

 fig. 10). Its migration follows the upward and dextral growth of the intes- 

 tine, which does not bend sharply upward along the posterior interray; the 

 radianal for a considerable time holds closely to the right-posterior radial, thus 



1 See foot-note, p. 81. 



