DEVELOPMENT OP AMPHIURA SQUAMATA. 145 



sible to me that the missing cell plasma of the oval nuclei 

 which are on the wall of the blood-vesselis to be found in the 

 blood fluid ; for this latter stains brightly, and always quite 

 fills the vessel. The aboral ring has, according to Hamann, 

 a different constitution. Its wall consists of well-marked 

 cells, and there are scattered cells in the " fluid.^' I believe 

 the suggestion has been made, though I cannot find the refer- 

 ence, that the aboral blood-ring results from a degeneration 

 of the rachis. I have myself seen a structure like what 

 Hamann describes in the large non-viviparous species, Am- 

 phiura Chiajii; which has, like most Ophiurids, a special 

 breeding season. Amphiura squamata, on the other hand, 

 breeds all the year round; and hence one can understand why 

 there should be no degeneration in its rachis. Why, however, 

 the degenerate part of a rachis should be called a blood-vessel 

 I fail to see. 



Kohler (9) has examined Ophioglypha texturata, and 

 has arrived at very curious results. I must, however, protest 

 against the practice of painting in colours the blood-vessels in 

 figures professing to give histological details. This mixing of 

 diagram and figure seems to me quite to beg the question. 

 Kohler fails to find the aboral sinus, but sees two prolon- 

 gations of the ovoid gland attaching themselves to the sides 

 of the madreporic plate. This I believe to be due to a mis- 

 conception of a section like my fig. 11, in which the gland is 

 cut tangentially, and the boundaries of the axial sinus might 

 simulate prolongations such as he describes. The enormous 

 shrinkage cavity one sees in his figure, and his failure to 

 detect the proper relations of the aboral part of the gland, 

 point, in my mind, again to imperfect preservation. The oral 

 blood-ring he finds to be constituted of a mass applied to the 

 dorsal and outer wall of the perihsemal canal, consisting of an 

 irregular meshwork of fibres with cells and brown granules. 

 This is certainly a curious structure to call a blood-vessel, 

 especially when it is remembered that, excepting the brown 

 granules, this is exactly the appearance of the ordinary decal- 

 cified tissue of an Ophiurid. The only reason Kohler has for 



