ElIABDITE-CELLS IK CEPHALODISCFS. 257 



So far, the results are the bodies described in the present 

 communication, a possible true sense-orsjan in the region of the 

 gill-clefts, and a large and undoubted gland situated on the 

 proboscis *. Descriptions of the two latter are left over for 

 the present. Of the material at my disposal sections were cut 

 in various planes and treated by various methods. The whole 

 coenoecium with the contained polypides was sectioned, as well as 

 also individual polypides orientated by the dissecting-microscope 

 in paraffin. The latter process, owing to the size of the 

 individuals, is by no means difficult, so that it is not necessary 

 to resort to Patten's method. So far as the purposes of the 

 present paper are concerned, the only method of staining found 

 to give really satisfactory results is Dr. Grustav Mann's ex- 

 cellent combination of meth) 1-blue-eosin f. The sections were 

 stretched on a slide previously treated with Paul Mayer's 

 albumen-fixative and covered with a film of water, and then 

 stained on the slide according to the directions given by Dr. Mann. 

 Successful preparations that have not been over-stained (when 

 properly decolorized for the rhabdites the general tissues are 

 almost unstained) show a perfect differentiation of the rhabdite- 

 " cells," so that their structure is somewhat easily followed by 

 examination with Zeiss's 1*5 mm. apochromatie lens in conjunction 

 with the compensating eyepiece No. 12. 



Historical. 



As is well known, after the return of the ' Challenger ' 

 Expedition, the bottle containing the specimens of Cephalodiscus 

 obtained in the Straits of Magellan was sent, with the collection 

 of Tuuicata, to Prof. Herdman. It then bore a label in the 

 writing of the late Prof. Moseley, stating that the animal was a 

 " compound Ascidian." Prof. Herdman examined it in the 

 winter of 1879-80, and mounted some preparations in different 

 ways (including the material referred to above), sufficient to 

 determine that it did not fall strictly within the group Tunicata, 

 and that its affinities were rather with what are now considered 

 the other Protochordata. He returned the stock to Sir Wyville 



* This apparently is not the structure referred to by Harmer (Zool. Anz. 

 1897), and I am not yet in a position to state its relation to the proboscis- 

 gland of Balanoglossus. 



t Journ. Anat. & Phys., toI. xxis. 

 LINN. JOURN. — ZOOLOGY, VOL. XXVII. 19 



