[XIV.] 

 THE ENTEROPNEUSTA. 



PART II. 



BY JAS. P. HILL, 



Demonstrator of Biology in the University of Sydney. 

 [Plates XIX.-XXIL] 



INTERNAL ANATOMY OP Ptychodera hedleyi. 



Proboscis. In the larger specimens examined the epidermis of 

 the proboscis has a thickness of about *13 mm. Below the two- 

 layered limiting membrane is the thin circular muscular layer, 

 with a thickness of -017 mm., i.e., slightly thicker than the same 

 layer in P. minuta.* 



Anterior to the central proboscis organs the longitudinal mus- 

 culature almost entirely fills up the cavity of the proboscis ; only 

 a small circular space filled up by spongy connective tissue is left 

 towards the centre of the latter. Below this space the centrally 

 situated longitudinal fibres form an interlacing bundle which 

 posteriorly, shortly in front of the central organs, divides into 

 two portions. These pass back laterally to the central organs to 

 take their origin with the more peripherally situated fibres from 

 the posterior wall of the proboscis. The longitudinal musculature 

 is not divided into radial masses. 



In this species the fibres of the dorso- ventral muscle-plate are 

 very strongly developed, with which fact is to be correlated the 

 flattened tongue-like form of the proboscis in preserved specimens. 

 Jn respect to the degree of development of the dorso-ventral 

 muscle-plate, P. hedleyi may be best compared with Balano- 

 ylossus kupfferi.^ 



In my preparations of this species it can be clearly seen that 

 numbers of the fibres of this dorso-ventral plate are inserted 

 directly into the limiting membrane of the anterior end of the 

 " notochord," which here is not covered by the glomerulus (fig. 6, 

 dsc.). Arising in the dorso-median line the fibres of this system 



* J. W. Spengel Die Entropneusten des Golfes von. Neapel, etc. 

 Fauna u. Flora des Golfes von Neapel, 1893, p. 17, etc. See ante p. 207. 

 f Spengel Joe. cit., pi. xiv., fig. 2. 



