450 



and the sinuses in connection with it , agree with his. He has not 

 seen the first rudiment of the gland at all. I have traced it back to a 

 single layer of cells forming part of the peritoneal lining of the coelom, 

 at a period when no axial sinus exists. M. Cue not taking it up at 

 a much later period (as his measurements of the animals sectionized, 

 shew), describes it as a growth in the interior of the axial sinus. He 

 states further that my results as to the relations of the sinuses sur- 

 rounding the ovoid gland agree with his. This statement I must pro- 

 test against strongly. I have shewn that the axial sinus surrounding 

 the gland, and the aboral sinus containing the genital rachis are derived 

 from involutions of the coelom. This was long ago suspected by Lud- 

 wig, but has been for the first time definitely proved by my investiga- 

 tions. Of the development of these sinuses M. Cuénot has seen 

 nothing whatever. He asserts in contrariety to Ludwig that the axial 

 sinus communicates with the stone canal, and in support of this asser- 

 tion gives a figure (Fig. 57 plate XXIX of the work cited). This is 

 perfectly correct : I have seen the same appearance in a large number 

 of sections. M. Cuénot has however given to it a totally wrong 

 interpretation. What he calls »Ampulla« is only a longitudinal section 

 of the pore canal as the columnar ciliated epithelium at once shows. 

 The true ampulla is here, as in Asterids and the nephridia of Peripatus 

 a thin walled vesicle lined by flattened cells. It is the opening of the 

 stone canal into this and not into the axial sinus which is seen in the 

 figure. These two thin walled spaces the axial sinus and the ampulla 

 are quite distinct and never communicate , as is easily seen when one 

 uses unbroken series of thin sections. I have been able, since writing 

 my first communication to this journal, to trace the ampulla back to 

 an anterior body cavity, as Bury has done for Antedon rosacea. 



M. Cuénot's »discovery« of the origin of the genital rachis from 

 the ovoid gland, in this case as in Asterids, is a mere guess based on 

 the similarity of the cells in the two organs. I am the first who has 

 traced the actual growth of the rachis from the gland. 



As to my denial of the »haemal« or »lacunar« system in this spe- 

 . cies, I can claim to speak wdth more authority than Mr. Cuénot on 

 this point , as I have tried and compared as to their results a large 

 number of methods of preservation and staining. With less perfect 

 methods than that which I finally adopted, I have often seen appea- 

 rances which might be mistaken for blood-vessels. 



The histology of adult Ophiurids is an exceedingly difficult sub- 

 ject and so far from the small size of Amphiura squamata unfitting it 

 for study, it is on this very account a favourable object for histological 

 investigation since the preserving fluids penetrate more rapidly and 



