46 SUMMARY OF CURRENT RESEARCHES RELATING TO 



fouuds the subgomis Pleurocioua to receive it. It differs from the 

 other species of the geuus in being attached throughout the whole 

 length of its left side from the posterior extremity to the base of the 

 siphons. The exterior layers of the tunic are of a greenish yellow 

 colour owing to the impurities attached to it, whilst the inner layers 

 are hyaline and transparent as in other species of the genus, besides 

 which certain figured bodies in the ground-substance of the tunic 

 contain a tolerably large vacuole. The i)eritoneal layer is inclined at 

 a highly oblique angle to the axis of the body. 



The second species, Ascidia elowjata, in its general aspect 

 approaches nearest to A. metula, from which, however, it is 

 distinguished by the greater length of the body. The latter, more- 

 over, is rounded instead of being flattened ; whilst the tunic is entirely 

 covered over with different foreign bodies, and the siphons, which 

 are scarcely prominent and of a red colour, only bear small and 

 obtuse tentacles. 



B. Polyzoa. 



Rhabdopleura.* — E. Ray Lankester commences his contribution 

 to our knowledge of this remarkable Polyzoon by an account of the 

 tubarium ; each tube is found to be built up of a series of rings, 

 and each ring is separately secreted and added to its predecessors by 

 the so-called buccal shield or prteoral lobe of the polypide ; the axis 

 is branching, but has no characters by which it can be distinguished 

 into primary, secondary, or tertiary portions. The substance of which 

 it is comi)osed is transparent and horny. 



Prof. Lankester finds that the polypide-stalk or gymnocaulus has 

 no relation to the funiculus of the Phylactolsematous Polyzoa, as was 

 supposed by Allman after an examination of imperfectly preserved 

 specimens. The buccal shield or disk acts as a locomotive organ, and 

 serves apparently to raise the polypide in its tube, and also, as has 

 been said already, as a secreting organ. On the aboral surface of 

 each lophophor arm there is a ciliated tubercle, which is possibly 

 related to the osphradium of the Mollusca, and it is, fui'ther, not 

 improbable that the lophophoral arms of the Polyzoa are the genetic 

 equivalents of the ctenidia of the Mollusca. 



There is a consistent and extensively developed internal (meso- 

 blastic) skeleton, which consists of two chief parts — the skeleton of the 

 lophophoral arms and that of the gymnocaulus. It is cartilaginous in 

 consistency. A precisely similar skeleton is to be found in CephalcH 

 discus. In addition to this new discovery, the author has been able 

 to make out the testis ; which is remarkable for its position, inasmuch 

 as it projects from the surface of the body. It has the form of a 

 much elongated sac, which is blind at one end, and opens at the other 

 by a special pore. It has nothing to do, as it seems, with a nephri- 

 dium, and belongs therefore to that class of gonads which the author 

 has previously distinguished as idiodinic, in contradistinction to 

 nephridinic. 



If Bhadopleura and Phoronis are both Polyzoa, that group can no 



* Quart. Journ. :\Iicr. Sci., xxiv. (1884, pp. 622-47 (.5 pis.). 



