676 



PROCEEDINGS OF THE ACADEMY OF 



[Dec, 



circular muscle, two steps being involved in the phylogeuy: first, 

 the inner circular layer breaks up into detached groups of dorso- 

 ventral fibres, then the latter turn out of their course and bend 

 around the intestine to form the encircling " oesophageal muscle." 



. o C Af 



^ iC M 



A 



Inf 



Diagram 5. — Cross section through the body of Zygcupolia, illustrating 

 the deflection of the dorso-ventral muscle fibres into the inner circular 

 muscle layer around the intestine — P.S., proboscis sheath; o.C.M., outer 

 circular muscle; Int., intestine; i.C.M., inner circular muscle; Dv.f., 

 dorso-ventral muscle fibres. 



This view is foreshadowed by Hubrecht (1887), p. 71, where 

 he says: " I will not at present attempt to decide whether any of 

 the muscular layers of the oesophagus, noticed both in Eapolia and 

 Cerebratulus' (PI. VI, fig. 9, ce.m.; PI. XIII, fig. 6, mto.), may 

 also be looked , upon as derivatives of this inner circular 

 layer. . , .;" and "Here, too [alluding to the Schizonemerteans], 

 I would be tempted to hazard a comparison between the absent 

 inner circular layer and the musculature of the proboscis sheath." 



To briefly summarize my views in regard to the presence and 



'The Cerebratulus here alluded to is C. corrugatm ^= Lineu8 corrugatus, 

 described by M'Intosh (1879). 



