RETORT ON THE ACTIN1ARIA. 103 



is determined by the line y, shows the same figure, but with this difference, that in this 

 case hollow spaces appear in the supporting lamella, which either lie as triangular gaps at 

 the bases of the ridges, or force themselves as fissures into the ridges themselves. These 

 hollow spaces, found in transverse section, correspond to the pouch-shaped invaginations, 

 which extend into the peripheral part of each radial swelling ; here and there I found 

 accumulations of cells in the spaces, — the remains of the epithelium lining them, which 

 unfortunately was badly preserved. In fig. 1 we have a transverse section taken through 

 the small folds at the beginning of the radial thickenings, along the line a. The 

 figures 1-3 show an irregular arrangement of the muscles, as they are sometimes 

 divided perpendicularly, sometimes obliquely, sometimes parallel to their direction. 

 This irregularity may be explained partly by the tortuous course taken by the beginning 

 of the radial swelling, partly by the fact that the muscular fibres, which originally 

 extended horizontally, have been slightly diverted from their straight direction by the 

 comb-like elevations of the supporting lamella. 



The oesophagus was too much injured to allow of its constitution being determined 

 by means of dissection. I was able, however, to examine pieces of it, recognisable by 

 their brown-violet colour, in a series of sections, and to make out openings which lie under 

 the oral margin and lead into the radial chambers. It seemed to me that there w T as an 

 opening surrounded by a swollen margin between every two insertions of the septa (fig. 4). 

 The openings are not all of the same size, as many of them can be recognised in a whole 

 series of transverse sections as long fissures, whilst others are only visible in three to four 

 moderately thin successive sections. They can hardly be considered artificial produc- 

 tions, in the first place, because the surfaces of the epithelium of the two sides pass 

 evenly into one another at the margin of the opening, and secondly, on account 

 of the comportment of the muscular system. The oesophagus of Polyopis striata has 

 exceptionally ectodermal longitudinal muscular fibres, which are only apparent in thin 

 transverse sections, as they are extremely fine. The muscular layer is thickly pleated 

 at the rounded margins of the openings, so that it may here be regarded as a sphincter 

 capable of closing the opening. 



The septa correspond to the longitudinal ridges on the surface of the wall, and are 

 therefore thirty-six in number ; they lie at perfectly equal distances from one another, 

 but are in pairs notwithstanding, as may be seen from the arrangement of the muscles. 

 Among them there are two pairs of directive septa (fig. 8) which are separated from 

 one another by eight pairs of ordinary septa. The latter vary very much in size, 

 although I was not able to observe' any arrangement in cycles of unequal value ; I 

 consider it most probable that we have here a tetramerous arrangement of the septa, but 

 that a pair of septa too many has been formed in one interspace on either side. Down- 

 wards the septa reach nearly as far as the aboral opening ; they are, however, of different 

 sizes, so as to present the figure given in fig. 11, /3. 



