Dr. W. B. Carpenter on the Development of Purpura lapillus. 19 



beg to make the following remarks ; premising that I speak not 

 only for myself, but for Mr. G. Busk, whose independent obser- 

 vations (made for the purpose of testing the value of mine) led 

 him to the complete adoption of the same view of the case. 



1. The absence of any definite membranous envelope around 

 the egg-like bodies, was, both to Mr. Busk and myself, a matter 

 of certainty. 



2. The existence, in certain of these bodies, of the ' directive 

 vesicles,' which MM. Koren and Danielssen now concur with me 

 in affirming, was most pointedly denied by them in their former 

 memoir. They bring no new observations to invalidate my state- 

 ment, that in the cases in which these bodies present themselves, 

 the segmentation follows a regular plan, tending to the pro- 

 duction of an embryo according to the ordinary Gasteropod type ; 

 but content themselves with affirming that the distinction which 

 I have drawn between the segmentation of the true ova and that 

 of the vitelline spheres is nugatory, 



3. Although MM. Koren and Danielssen spoke in their first 

 memoir of having only occasionally met with one of the embryos 

 developed from a single ovum, they now admit that several such 

 embryos are usually to be found in the capsule before the act 

 of conglomeration has commenced; thus again confirming my 

 statement as to a fact of fundamental importance. They do not 

 offer any explanation of the ordinary presence of these small 

 embryos, which is altogether meaningless, if (as affirmed by 

 them) they speedily perish, but which is fully explained (on my 

 view of the case) by their subsequent expansion into large em- 

 bryos through the ingestion of the supplemental yolk. I have 

 nowhere said, as is imputed to me, that all the bodies enclosed 

 in the capsules are " anatomically and physiologically alike ;" on 

 the contrary, I contend that although there is originally no 

 perceptible structural difference between the true ova and the 

 vitelline spheres, a definite physiological difference manifests 

 itself from the very commencement of the process of seg- 

 mentation. 



4. MM. Koi*en and Danielssen impute to me that I have 

 (under the influence, as they assume, of a preconceived hypo- 

 thesis) affirmed the existence of a mouth and a ciliated oesophagus 

 in the small embryos, and. have given delineations of these 

 organs, without any other foundation than my own imagination, 

 having mistaken for the oesophagus the foot in an incipient 

 stage of development. It is not a little strange that if / have 

 been deceived in this matter, so accurate and cautious an ob- 

 server as Mr. Busk should have not only followed me in this 

 error, but should have actually made the very drawings whose 

 truthfulness is challenged. That my eyes should have deceived 



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