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



The splanchnic epithelium of the proboscis coelom is not everywhere 

 distinct, but it becomes particularly definite in the ventral csecum referred 

 to above. This is an outstanding feature of all sections through this 

 structure. The cells are very regular in appearance and columnar or often 

 cubical, with large nuclei which stain intensely. The ventral ca2cum 

 projects, of course, into the buccal cavity, where it appears as a small but 

 very distinct protuberance. It is the structure which was named the 

 " blumenkohlahnliches Organ " by Spengel, on account of its lobose appear- 

 ance in Ptychodera errtfthrcea. Willey termed it the Racemose Region, and in 

 several varieties of Ptychodera flava it appears to possess some few small 

 round elevations. Such is not the case in Pt. pelsarti — at least, in the 

 specimens examined. The epithelium of the buccal cavity is also modified 

 where it covers this organ, making it still more conspicuous in sections. 

 One characteristic feature of the ventral proboscis caecum (and consequently 

 of the so-called Racemose Organ) of Pt. pelsarti is that it is very muoh 

 compressed laterally (fig. 8), the septum itself consisting merely of two 

 layers of epithelium (Splanchnotheca) with a most delicate layer of tissue 

 and blood-spaces between them. The total thickness of the septum is only 

 •03 mm. The relation of the nuchal skeleton to the ventral proboscis csecum 

 is another feature of some importance, and will be referred to below. 

 The anterior border of the ventral septum runs obliquely backwards from 

 the central complex. 



Proboscis j^ores. 



There are two proboscis pores, as in PtycJiodera flava varieties, opening 

 one on either side of the middle line. Willey states (1891) that Pt. flava is 

 characterised by the constant occurrence of paired proboscis pores, although 

 considerable vai'iation seems to exist in the manner of communication 

 between the pores and the proboscis coelom. Six variations were described, 

 but in all cases there were two pores — two actual openings. 



The proboscis pores open into terminal ectodermal vesicles, which are 

 connected by tubes with the dorsal ccBlomic canals. Now, in Pt. pelsarti, as 

 in Pt. flava, the proboscis pore is a wide orifice almost equal in diameter to 

 the terminal vesicle itself (PI. 11. figs. 8 & 9, V.p.p.). Tn two specimens 

 examined by serial sections there was some variation in the coelomic canals. 



In specimen A two proboscis pores were to be seen, one of which com- 

 municated with the coelom directly. The other pore also opened into a 

 terminal vesicle, but this was not in communication with its corresponding 

 dorsal coelomic canal. The two cavities were separated by chondroid tissue 

 (fig. 9). This condition is somewhat like that of Series II. of Willey. 



In specimen B, both sides of the animal were similar, the dorsal coelomic 

 canals running without any block into terminal vesicles, which opened by 

 proboscis pores to the exterior. 



