1901.] NATURAL SCIENCES OF PHILADELPHIA. 667 



the circular muscle, in the iuuer longitudinal layer. At the pos- 

 terior end of the dorsal lobes the followiug changes may be uoted. 

 The circular fibres, figs. 19, 20, CM., at first all ruu along the 

 inner surface of the end of the dorsal ganglion and beginning of 

 the cerebral organ, then a few fibres bend out and curve around 

 the sense organ on its outer side, until finally all the muscle fibres 

 lie ou the outside of the cerebral organ, fig. 21, CM. The ven- 

 tral ganglia lie as before, outside the circular muscle. 



Just in front of the mouth a strong baud of muscle, fig. 21, 

 H.M., runs from side to side, beneath the rhyuchocoel and above 

 the median blood vessel. 



In the oesophageal region, fig. 22, there is nothing unusual in 

 the structure of the muscle layers; the outer longitudinal, o.L.M., 

 is the thickest, and next the circular, CM. This arrangement 

 continues past the nephridia into the region of the expanded rhyn- 

 choctel, where all layers of the body wall are greatly stretched, 

 and consequently very thin. 



A short distance anterior to the middle intestine the rhyncho- 

 coelomic dilation ceases aud the diameter of the rhynchocwl is about 

 equal to that of the oesophageal region, while its walls are fre- 

 quently folded and constricted. In this part of the body the cir- 

 cular muscle of the body wall becomes greatly thickened (see Plate 

 XLIV, fig. 62, CM.). 



Inner Circular Muscle. — Fig. 23, Plate XLI, is a cross section 

 of the body just antecior to the beginning of the middle intestine. 

 The diameter of the body is less than in the (esophageal region 

 (of. fig. 22)j and much less than in the great exjianded portion 

 which is not figured. The outer longitudinal muscle in fig. 23 

 needs no description ; the circular muscle is relatively thicker than 

 in the anterior part of the body, but not greatly enlarged. The 

 circular muscle of the proboscis sheath has increased greatly in 

 size and some of its outer fibres ruu ventrally, making a baud of 

 circular muscle, i.CM., that encircles the stomach, S. Other 

 fibres, apparently from the circular muscle of the body wall, join 

 with these, running dorso-ventrally, and crossing the inner longi- 

 tudinal layer dorsal ly and ventrally. In short, an inner circular 

 muscle layer is here present; and muscular crosses occur between 

 it and the outer circular layer, both dorsally and ventrally (see 

 fig. 23, D.m.cr., V.m.cr.). A few sections posterior to the one 



