20 Dr. W. B. Carpenter on the Development of Purpura lapillus. 



me, when I saw, during the prolonged observation of the same 

 individuals, yolk-segments actually pass down this oesophagus, 

 and their bodies augment in bulk, does not strike me as very 

 probable. 



5. It is not a little significant that, puttiug aside the fore- 

 going difference, the figures given by MM.Koren and Danielssen 

 to illustrate their second memoir bear far more resemblance to 

 mine, than they do to those by which their first memoir was 

 illustrated. This fact, of which any one who compares the 

 three sets of figures may readily satisfy himself, cannot but throw 

 some doubt over the trustworthiness of the figures and descrip- 

 tions originally given by those authors. 



6. The contractile vesicle which was described and figured by 

 MM. Koren and Danielssen in their first memoir as the heart, 

 and which is distinguished by its projection from beneath the 

 mantle during the middle period of development, I again atfirm 

 (and this without the slightest hesitation) not to be the 

 heart. AVith the aid of the achromatic condenser, I was able to 

 recognize what the presence of a distinct auricle and ventricle 

 showed to be unmistakeably the heart, much deeper in the cavity 

 of the mantle ; and that these observers should not have recog- 

 nized it, may be due to their not having transmitted a sufficiently 

 strong light through the semi-opake body of the embryo. Al- 

 though the reference they make in their second memoir to some 

 other conti'actile vesicle (kidney ?) would seem to imply that they 

 had recognized (as I have done) two distinct contractile organs, 

 they have given no evidence of having done so. 



I will not take upon myself to affirm that I have made no 

 errors in my description of the process. Those who may take 

 the trouble to consult my original memoir, will find that there 

 are certain parts which I do not consider myself to have fully 

 made out. But I cannot at present entertain any doubt as to 

 the general facts of the case ; and I submit that the admissions 

 now made by MM. Koren and Danielssen go to strengthen my 

 view of it. It is obvious that the main point to be decided by 

 further observation is, whether I am right in affirming that in 

 embryos developed from single ova, a ciliated mouth and oeso- 

 phagus exist, down which yolk-spherules can pass ; or whether, 

 as MM. Koren and Danielssen assert, I have mistaken for the 

 oesophagus the incipient foot. I would suggest to any observers 

 who, during the present season, may have the opportunity of 

 studying the development of Purpura (at Tenby the egg-capsules 

 are so abundant that they may be gathered by the handful), 

 that they give their special attention to this point, and that they 

 endeavour so to place the embryos under the microscope, as to 

 be able to look at the mouth from the front, as well as from the 



