Royal Microscopical Society. 213 



discloses indistinct moleciiles ; in many cases, the addition of aceti 

 acid, besides giving it a coarsely granular appearance, causes a feM 

 transverse lines to become visible, as if it were about to divide into 

 segments. 



According to Dr. Fol, this body secretes a glairy mucus, which 

 mixes with the food as it passes down the pharynx, and, therefore, 

 belongs to the digestive system. I have not observed this secretion, 

 neither have I seen the pair of styles with which the same authority . 

 remarks that the endostyle is provided. 



There are two apparently glandular bodies, one on each side of 

 the endostyle, instead of only one, as I supposed in my last paper, 

 for reasons which will appear presently ; in structure they so far 

 resemble the endostyle as to show obscure indications of molecules 

 in their substance ; it is noticeable that in small specimens these 

 bodies are larger in proportion to the size of the endostyle than in 

 large specimens ; perhaps they have some function in the economy 

 of these animals analogous to certain foetal structures in the verte- 

 brata, e. g. the thymus ; their position, also, it may be remarked, is 

 homologous. 



Four openings pierce the integument, but only two need be 

 noticed at present ; these are the ciliated branchial openings. In 

 my last paper I mentioned that there existed only one of these 

 openings; this mistake arose from the circumstance that all the 

 specimens were examined on the side, this being the position which 

 the animal invariably assumes when slightly held by the covering 

 glass, and when this is the case, one branchial opening conceals the 

 other (the same thing occurs in the case of the glands just men- 

 tioned). It so happened, in my investigations last year, that 

 when the creatm-e had been sufficiently examined in this position, 

 it was out of my power to procure any fiu'ther specimens, so that I 

 was unable at the time to correct misapprehensions caused by want 

 of variety in position. The branchial openings are situated on the 

 haemal side of the pharynx ; they are rather long tubes, having a 

 direction backwards, hsemad, and shghtly towards the middle line. 

 The internal openings are larger than the external ; the fonner are 

 circular in outline, and are provided with a circlet of strong cilia, 

 which, when in action, gives a figure resembling the engine-turning 

 on the back of a watch, or the drops of water from a revolving 

 wheel. The circumference of these openings is enclosed by two or 

 three strong circular fibres, outside of which a circlet of pentagonal 

 cells occurs ; each of these cells is pro\aded with a clear spot 

 resembling a nucleus ; five of them can be counted on the anterior 

 part of the circumference of the openings, which is all that is visible 

 on the hfemal view of the animal. 



The external openings are quite plain, and unprovided with ciHa ; 

 they are smaller than the internal, somewhat oval in shape, and are 



