46 HENEY MCELDEREY K NO WEE 



the older larva is recognized as having reached another well- 

 defined stage, to be numbered 4 in the series (Liu-Li's stage 3 ; 

 Pollister's late 22), and illustrated in figures 14, 15 and 21 of 

 the present paper. 



A conical or pear-shaped body, with intestinal bend, differ- 

 entiates these larvae readily from the tubular form of the 

 previous stage (stage 2, fig. 2) the new cone-shaped figure 

 being produced by enlargement of the liver and stomach (now 

 free of yolk) anteriorly in the base of the cone, with reduction 

 of the hind-gut to a narrower tube in the prolonged apex. 

 Distention of the abdominal cavity adds to the contour, while 

 enlargement of the head, through the growth of the operculum 

 and expansion of the branchial cavities, broadens the base of 

 the cone. The contour of the head is also extended by addi- 

 tion of a peripheral zone of mesenchyme, which has spread 

 out between the organs and the surface layers. 



The pronounced S-shape coil in the digestive tract in the 

 late larva of the period, stage 4 (illustrated in figs. 14, 15, 21) 

 results from rapid progress of the two primary bends into 

 deep folds which separate the stomach in front and hind-gut 

 posteriorly from the large mid-section of the gut lying across 

 the abdominal cavity as a yolk-filled bag. In this process the 

 stomach, seen first as a small local extension off the left end 

 of the yolk tube (fig. 2a), is separated by a deep fold in the 

 next stages and comes to lie across from left to right as shown 

 for stage 4 in figure 21. The connection with the mid-gut is 

 retained at the right and the yolk tube continues from the 

 junction in a sharp turn ventrally across to the left, to end 

 in the hind-gut. Here the hind-gut fold makes a final turn to 

 the left in another strong bend (figs. 14, 15, 21). In most 

 specimens of this fourth stage, the gut is still quite distended 

 with yolk, and rather quadrilateral in shape, as shown in the 

 accompanying figures ; but in the bullfrog and in toad larvae 

 of the stage, less yolk in the gut results in a more tubular 

 coil. In both stages 3 and 4 of frogs the larva is still about 

 the same length as in the previous stage (between 7 mm. and 

 8 mm. in R. palustris), but, as noted, decided increases are 

 present in other proportions. 



