ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 761 



ganglion cells, and motor nerve-fibres from those in the wall of the 

 ampullaj. 



Further, it may be regarded as probable that the central nerve-pentagon 

 has a diiferent function at the angle whence the radial medulla arises than 

 in the commissures ; perhaps there are there a larger number of ganglion- 

 cells ; these points are distinguished physiologically by being the seat of 

 higher psychical functions than is the radial medulla. 



The explanation of the consensus which the five-rayed or many-rayed 

 animal exhibits is, it is probable, to be explained, not by supposing there is 

 a permanent " central soul " governing the five separate " souls," but that 

 at one time one, and at another time another, central stimulus has the 

 upper hand ; the Echinodermata must be regarded as possessed of what is 

 ordinarily called psychical activity — for Asterids and Ophiurids have sensa- 

 tion, will, understanding ; what is peculiar to them is that mind or " soul " 

 is fivefold or manifold, has five (or more) similar substrata which are in 

 close organic connection with one another. Only so long as this nervous 

 substratum is uninjured is the psychical activity able to act in harmonious 

 co-ordination. 



Circulatory Apparatus of Ophiurids.* — Dr. E. Koehler finds it 

 necessary to distinguish in the circulatory apparatus of Ophiurids a vascular 

 and an aquiferous system together with a system of perihaemal canals. The 

 aquiferous system, the study of which presents no difficulties, consists of an 

 oral circle provided with Polian vesicles and giving off radial trunks ; it 

 communicates with the exterior by means of the sand canal. The system 

 of perih^mal canals consists of the oral circle, the radial canals, and a space 

 which incloses the madreporic gland ; the canals are divided by a partition 

 into two cavities, in one of which are lodged the nerves and the vascular 

 trunks; the radial canals give off lateral branches which open into the 

 dorsal cavity of the arm, which is the continuation of the general cavity ; 

 and it is in this way that the periheemal canals, which are not direct pro- 

 longations of the ccelom, and are even developed quite independently of 

 them, communicate with the general cavity. The fluid found in this cavity 

 contains the same elements as that which circulates in the perihaemal canals. 



The vascular system presents quite special characters ; instead of having 

 a free lumen, the walls of which are lined by an epithelium forming a very 

 definite layer, it consists of a series of formations made up by a special 

 tissue ; in this there are anastomosing fibres, in the midst of which there 

 are developed cells whose protoplasm is charged with pigmented granula- 

 tions, such as are found in the coelom. This tissue is arranged in the form 

 of fibres which make up the oral vascular circle, and the radial vessels • in 

 the madreporic interradius, however, it forms an organ of considerable size 

 — the madreporic gland. These structures are always inclosed in the 

 schizoccelic spaces, the whole of which forms the system of perihtemal 

 canals. The vascular system of Ophiurids may, therefore, be considered as 

 a collection of structures diiferentiated within the perihsemal canals which 

 have a complicated structure, and form tissues of the glandular type in 

 which there are developed elements which are analogous to those of the 

 coelom. It would appear then that the chief function of the so-called 

 vascular system of Ophiurids is to produce these elements ; in fact, cells 

 with pale and irregular protoplasm are very numerous and closely packed 

 in the central parts of the madreporic gland, where they appear to multiply 

 actively ; thence they pass towards the peripheral region, and as they do so 

 they become charged with pigmented granulations ; there is nothing to lead 



» Ann. Sci. Nat.— Zool., ii. (1887) pp. 101-58 (3 pis.). 



