resemblance of the tentacular arms to the so-called Lophophore of the freshwater Polyzoa). 

 r Fhe next year appeared Allman's treatise .,on Rhabdopleura, a new form of Polyzoa from deep 

 sea dredging in Shetland" 1 ; and my Father, as well as myself, at once recognised in the species 

 therein described and delineated, Rh. Normanni, a form closely agreeing with the Halilophus 

 mirabilis, but which evidently, from the form and attachment of the Polyzoarium, must belong- 

 to a different species from ours. Allman's communications concerning the organisation of the 

 animal shew indeed, as will appear from the sequel, many essential differences from what I 

 have had occasion to observe in our northern form; so that if these communications were 

 in reality* correct, there could scarcely be any doubt that both forms were also generically 

 distinct. But the fact is that Allman has only had the opportunity of examining specimens 

 preserved in spirit; and both my Father and myself know from experience how extremely 

 difficult it is to obtain results with specimens in this state, and what imperfect and false 

 notions may thus be formed of the animal's real structure. Taking this into consideration 

 we may really be astonished that Allman has been able to see so much as he actually has 

 seen, and that h-e has not misunderstood the animal's organisation in a greater degree than 

 appears from his description and delineations. Allman has indeed seen in the Ehabdopleura 

 a very aberrant form of Polyzoa, but is far from having apprehended that the form is ab- 

 normal in so high a degree as it is proved to be, according to investigations which I have 

 executed with the utmost care and minuteness. 



With respect to the method of examination, there is little or no use in dissecting so 

 small and fragile an object as the animal of the Rhabdopleura, even if the finest imaginable 

 instruments are employed. It is therefore necessary to study the animal entire as it is, or 

 at most after separating the individual animals from their cells or tubes, which, as will be 

 seen, may be done with the greatest ease in operating on the living colony. In order to get 

 a better and sharper view of certain parts, I have found it very useful to effect a gentle com- 

 pression of the animal between 2 glass plates, but so that the pressure can be moderated at 

 will, increased or diminished. To this end I cemented a thin glass plate to the upper arm 

 of my compressorium, by which means the desired result was obtained far better than by the 

 use of the so-called aquatic boxes". Moreover most of the parts of the living animal may 

 be easily examined without pressure, and without even taking the animal out of its cell. A 

 colony, or part of one, can be placed under the microscope, and the most important parts will 

 plainly be seen through the transparent walls of the cells, even if the animal has not stretched 

 itself out of the aperture. 



Besides the outer chitine-like tube with its off-shoots or cells (Polyzoarium) there may 

 be distinguished in the animal under consideration the following principal parts. 1. the Po- 

 lypidc itself, which again shews 3 principal parts a) the body; b) the tentacular arms and 

 <) the bucal shield; 2. the contractile cord: and 3 the n.rial cord. We shall treat each of these 

 parts separately. 



Quarterly Journal of microscopical science. Vol. IX. 1869. p. 57-63. pi. 8. 



