ANATOMY OF ARENIOOLA ASSIMILIS. 785 



oesophageal connectives, Uie pharynx, tlio circular and longitudinal muscles. 

 The nuclei of the muscle-fibres have been omitted, x 210. 



PLATE 37. 



Tig. 23.— Transverse section of the anterior end of a specimen of A, 

 assimilis, from Uschuaia. The section passes through the anterior part of 

 the brain at the point of origin of the oesophageal connectives. The two 

 anterior cerebral lobes are seen in the prostomium in close relation to its 

 epithelium ; bands of nerve-fibres (N.) may be seen passing from the latter 

 into the brain. The cells in the brain are represented by the dots shown in 

 tile figure. The spaces seen in the brain and in the subepidermal tissue are 

 canaliform prolongations of the coelomic cavity. On the left the section has 

 passed somewhat obliquely through the skin, and shows the numerous 

 branches given off from the oesophageal connective, and ending in the basal 

 part of the epidermis. The dots in these nerves represent the nerve-cells 

 which are present. Immediately to the left of the prostomium is the external 

 opening of the otocyst (b\vt. Op. OL), the tube being cut through along a con- 

 siderable part of its length; a transverse section of the inner part of the tube 

 is seen just ventral to this. In the lower part of the figure the buccal mass 

 is seen cut across; the elevations of the epithelium (Pap.) shown are the 

 papillffi of the "proboscis." Tlie nerves {N. Bucc.) whicli supply these are 

 shown. Note the strong musculature of the buccal mass, x 30. 



Fig. 23. — Transverse section of the middle portion of the brain of a speci- 

 men of A. assimilis var. affinis, from Otago Harbour. Only the left half 

 of the section is drawn; the median plane is indicated by the two vertical 

 lines. In the upper part of the section the intimate relation of the prostomial 

 epithelium and the brain may be observed; the ganglion-cells extend up to, 

 and lie among the bases of, the epithelial cells. The dots in the brain repre- 

 sent the nuclei of small nerve-cells, which are usually arranged in groups or 

 clusters. The large cells in the middle of the figure show the form and posi- 

 tion of the larger ganglion-cells of the brain. Their processes extend down- 

 wards into the neuropile, where they branch. Note the numerous fibres 

 passing from the left half of the brain across the middle line to the right, form- 

 ing the middle cerebral commissure. The isolated cell on the right side is 

 drawn from another section, x 210. 



VOL. 46, PAK'l' 4. NEW SERIES. FFP 



