176 H. V. WILSON AND BLACKWELL MAHKHAM 



take these up in order, as affecting the ahnientary eanal, s])inal 

 cord, notochord, myotonies, and pronei)hi-os. 



Alimentary canal. The anterior end and the pharyngeal re- 

 gion of the ahmentary canal have the usual anatomy, appearing 

 as parts of a wide, straight passage. This comes to an end at 

 the anterior limit of the yolk mass. The latter in this region is 

 found to be excavated by numerous tubular channels, round 

 \\hich the cells are arranged in epithelial fashion. A few other 

 similar tubes with less yolk in the cells lie at the surface of the 

 mass (fig. 5). It is possible to trace some interconnections be- 

 tween these, and the tubes are perhaps all interconnected, rep- 

 resenting an alimentary canal in the making. A remnant of the 

 original archenteron persisting as a shallow slit-like cavity, which 

 extends well into the yolk and connects with the exterior round 

 the right lip of the blastopore, is present in this region (fig. 5, 

 arch): It connects with, at any rate some of, the tubular chan- 

 nels above referred to. Possibly it forms the terminal, anal, 

 part of the alimentary canal which is in process of differentiation. 

 The posterior and much the greater part of the yolk mass re- 

 mains as solid and compact and undifferentiated as in a gastrula 

 stage. 



It is clear that in this larva an alimentary canal was in process 

 of formation by a method different from the normal. The de- 

 parture is probably adaptive to the continued presence of the 

 yolk mass. In the figurative language of vitalism, the embryo 

 makes an effort to form an alimentary canal, although the cus- 

 tomary road to that end is not open. Moving slightly away from 

 \'italism, we seem to see the destined end of the ontogeny work- 

 ing backward as a cause, a philosophic idea which certain embry- 

 ological writers (cf. Jenkinson's admirable book, '09, p. 20) have 

 in recent years shown a willingness to adopt into our family of 

 concepts concerning the processes at work in ontogeny. To in- 

 voke such retroactive influences may, as Jenkinson says, in the 

 end prove necessary, but on the other hand it may not. The 

 fact is that while the idea of individual adaptation or regulation 

 in ontogenetic processes is now familiar to us, the detailed facts 

 (comparative and experimental) of any particular set of cases 



