96 PROF. W. J. DAKIN ON A NEW SPECIES OF 



obliquely backwards. A lumen may be traced far (juite a distance — at least, 

 in the most anterior roots. The histological structure is practically the same 

 as that of the dorsal wall o£ the nerve-cord. 



Collar Epidermis. 

 The collar epidermis is divisible^ as in other species of Ptychodera, into jfive 

 zones (PL 10. fig. 2). The extent of these has been previously noticed. It 

 will suffice here to mention that the second, third, and fourth zones are 

 somewhat similarly constituted, and in section stain darkly with hsema- 

 toxylin owing to the numerous gland-cells present. The fourth zone of the 

 collar is, however^ the most markedly glandular region of the animal's 

 epidermis and stains very intensely with hsematoxylin. The fifth region is 

 very free from dark staining cells. 



Collar Coelom. 

 The cavity in the anterior half of the collar is reduced, a considerable 

 amount of connective tissue being present between the outer epidermal 

 muscle-layers and those underlying the wall of the alimentary tract 

 (tig. 2, C.tis.). Behind the anterior region there are numerous transverse 

 muscle-fibres arranged in radial bundles (PI. 11. fig. 10, R.nms.), and the 

 cavity — collar coelom — is thus split up somewhat. 



A well-developed dorsal septum is present, in the specimen examined, 

 posterior to the second root of the collar nerve-cord (fig. 10, D.Sept.). On 

 the ventral side of the collar a longitudinal space is present, into which 

 project folds with vessels belonging to the ventral vascular plexus (fig. 10^ 

 V.plea;.'). No ventral septum appears to be present. 



Collar Canals. 

 The collar canals have the same characters as those of many other 

 described species of the Ptychoderidse, i. e. ft. /lava, Glossohalanus minuta, 

 Bala7ioglossus australiensis, etc. 



Brancliio-ge7iital Region. 



Reference need only be made to a few points here, for the general 

 structure is in agreement with that of the other known species of Ptycltodera. 

 The gonads extend forwards in the genital pleura up to the most anterior 

 gill-clefts. The pleura are well developed and arise somewhat deeply, but 

 certainly not so far ventrally as is the case in some other species of 

 Ptychodera. There is, moreover, a very striking difference between trans- 

 verse sections of Pt. flava (and apparently its varieties) and Pt. pelsarti, the 

 sections being taken through the branchio-genital region in each case. The 

 difference lies in the relative area of the branchial and oesophageal divisions 

 of the pharynx. In Pt. /lava [the branchial region predominates over the 



