432 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Morphology of Ophiurids.* — Dr. 0. Ilamann lias published a pre- 

 liminary account of his observations on the morphology of Ophiurids. 



(1) Central or Peripheral Nervotis System. — This differs from that of 

 Asterids by lying in the mesoderm. When sections are made of a nerve- 

 trunk it is seen that its cellular investment is not always the same, the 

 cells being sometimes in one and sometimes in several layers. There is 

 only one layer at the points where the brauchlets are given off to the 

 pedicels. The cells are very small, the cell-substance can scarcely bo 

 seen, and there is a spherical nucleus. In the intermediate regions the 

 cells aro arranged in several layers, but no supporting fibres can be 

 made out, and there is nothing which prevents our regarding them as 

 ganglion-cells. This would show that the Ophiurids are the most highly 

 developed of Echinoderms, for a segmentation of their nerve-trunks can 

 be made out. Another peculiarity is the presence of a nearly circular 

 blood-lacuna in the middle line of the nerve-trunks ; this passes towards 

 the centre, where it meets with a circular blood-lacuna ring, which lies 

 internally to the nerve-ring. Of the branches given off from the central 

 trunks the author recognizes nervi costales, which pass to the intercostal 

 muscles, and nervi epitheliales which branch in all directions. Below 

 the epidermis there is a nervous plexus which may be distinctly seen on 

 both arms and disc. In no group of Echinoderms is there such an ex- 

 quisitely developed nervous system. The large number of epithelial 

 nerves, and the extension of the sub-epithelial nerve-plexus, are closely 

 associated with the great power of rapid movement possessed by these 

 animals. 



(2) The Wandering Germ-cells and their Sites of Maturation. — The 

 ova and spermatozoa arise from primordial germ-cells, which make 

 their way into the developing genital saccules, and then become differen- 

 tiated. The author has discovered a genital tube, which extends partly 

 into the dorsal wall of the disc and partly into the walls of the genital 

 pouches. This tube is placed on a cord of connective substance and is 

 surrounded by blood-fluid, which flows into the lacunas and clefts of the 

 cord. The latter lies in a schizocoel space. In structure this genital 

 tube closely resembles that of Crinoids. 



(3) The Dorsal Pore. — The author thinks that an association of 

 Ophiurids with Asterids in one group can only be justified on the ground 

 of their external similarity ; otherwise the Ophiurids are more closely 

 allied to the Crinoids. In an adult Ophiolepis albida, Dr. Hamann has 

 discovered an excentrically placed dorsal pore. The body- wall is 

 traversed by an infundibulum which puts the coelom into communica- 

 tion with the sea-water. The inner wall is quite flat, and is lined by 

 ciliated cells, which on the one hand pass into the outer body-epithelium, 

 and on the other into the epithelium of the enterocoel. This pore has 

 nothing to do with the stone-canal, but is to be compared rather to the 

 calycinal pores of Crinoids. 



(4) Schizoccel Pores and Blood-lacunar System. — In 0. albida the 

 author finds a space which passes partly into the dorsal wall of the 

 body-disc and partly into the walls of the genital pouches. In this 

 there lies the blood-lacuna ring, which takes the same course and lies in 

 a septum of connective tissue. The blood-fluid flows into the peripheral 

 lacunae of this septum. These lacunas are best developed in the dorsal 



* Nachr. K. Gesell. Wiss. Gottingen, 1S87, pp. 394-400. 



