ON THE ZOOLOGICAL i>TATION AT NAPLES. 371 



With regard to question No. 1, it seems to me probable that the 

 animals described as ' StepJianoscijphus mirabilis ' by Allmau, and ^ Spoiujicola 

 fistidaris ' by Schulze, are one and the same. 



I am enabled to endorse Professor Schulze in every statement he has 

 made, and have very little indeed to add to his work. 



The only points on which I can as yet extend his excellent paper 

 are -with regard to the way in which this animal retracts, and to the 

 structure of the ' Liingswiille ' or longitudinal ridges. 



First, as to retraction. The entire body-wall for the first half mm., 

 more or less, folds over inwards, like the finger of a glove when it is 

 pulled inside out, bringing the tentacles into the interior of the animal ; 

 the membi'anous hypostome, which is so diflBcult to see that it might 

 easily have been missed, even by such an excellent observer as Professor 

 Allman, is pressed close against the sides of the body some way down, 

 leaving apparently a canal lined with endoderm, which appears to be in 

 the body- wall. 



This I take to be what Professor Allman mistook for a circular canal. 

 The tentacles are much retracted, and either lie pointing outwards, or 

 can be again extended deep down into the interior of the animal, when 

 no doubt particles of food entangled in the thi'ead-cells, with which the 

 tentacles are plentifully covered, are digested by the endoderm cells. 



When a careful sei'ies of transverse sections are cut, first (as might 

 be expected) there is a solid ring of ectoderm, then there appears 

 endoderm in the middle between two circular layers of ectoderm, next 

 a circular space is seen dividing the endoderm into two layers, which 

 closely approximate to the two layers of ectoderm, forming an apparent 

 circular canal lined with endoderm. The interior space lined with 

 ectoderm is filled by transverse sections of tentacles. Still deeper 

 sections are reached showing the tentacles given off from the internal 

 layer of ectoderm with the approximated layer of endoderm running out 

 into and forming the solid centre of each tentacle ; below that, unless 

 the tentacles have been projected downwards into the body of the 

 animal, transverse sections of them cease, and the two layers of the 

 endoderm again come to be closely approximated ; a few sections further 

 on the internal layer of ectoderm ceases, and only an external layer of 

 ectoderm and a layer of endoderm, separated by a layer of supporting 

 lamella, remain. 



Between the ectoderm and endoderm there is always a layer of clear 

 colourless supporting lamella, bat in the upper parts it is very thin and 

 in many cases hardly to be distinguished. But after the limit of in- 

 vagination is reached, the layer of supporting lamella becomes much 

 more distinctly seen ; and here also two layers of longitudinal muscular 

 fibres make their appearance, one on each side of it. These layers of 

 muscular fibi-es, proceeding lower with the series of sections, join each 

 other at four places, forming, as it were, four oblong pieces of supporting 

 lamella surrounded by muscle fibres. These oblong pieces gradually become 

 more circular and draw away from each other, and their centres are 

 filled with peculiar long-shaped cells, which are apparently thread-cells 

 in various stages of development. Round these the endoderm lining the 

 whole of the internal cavity makes four folds which project inwards 

 into the interior of the cavity, the space between the muscle fibres and 

 themselves being filled with the clear colourless supporting lamella. 



These in transverse and longitudinal sections look very like longi- 



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