] 2 Echinoderma. 



given by Kohler [see Bericht for 1883 I p 131], except that H. found no longi- 

 tudinal muscular fibres in the gullet. The spaces in the connective tissue layer 

 contain coagulated blood with its characteristic cells ; and Hoffmann's denial of 

 the presence of ciliated epithelium is a mistake as regards the rectum. - - In quite 

 young Urchins (1-2 mm diameter) the dorsal schizocoel ring contains a circular 

 genital tube uniting the 5 rudimentary ovaries or testes which have budded 

 outwards from it , and like it are full of germ-cells . In older Urchins this genital 

 tube atrophies and its place is taken by a thickening of the wall of the dorsal 

 schizocoel ring in which the anal blood-lacunar ring is developed; extensions of 

 this pass outwards on to the principal genital ducts and their branches, so that the 

 entire organ is surrounded by blood spaces. The germ cells which will become 

 ova increase in size pushing the adjacent cells before them so as to form a kind 

 of follicle epithelium, but they eventually lose this cellular investment and acquire 

 a vitelline membrane. The reticular connective tissue which forms the 

 organic basis of the calcareous plates is of the kind described by Haeckel as Cla- 

 thralgewebe. It is formed by the union of the processes of numerous stellate cells, 

 the calcified ground substance of the tissue occupying the meshes of the network. At 

 the sutures of the plates the structure becomes more fibrous. The ligament join- 

 ing the head of a pedicellaria to its calcareous support is extremely elastic and 

 consists of a finely granular gelatinous tissue which is surrounded by longi- 

 tudinal muscle fibres. The muscles of a spine or the adductors of a gemmi- 

 forin pedicellaria consist of homogeneous, strongly refractile, nucleated fibres 

 which exhibit a fine longitudinal striation indicative of fibrillation. These are 

 mesenchymatous in origin , but do not differ essentially from those in the wall 

 of the gut which are of an epithelial character. Fibres with cross striation occur 

 in the adductors of the buccal and tridactyle pedicellariae. They retain the nu- 

 cleus and some finely granular remains of the formative cell and have a delicate 

 sarcolemma. The whole musculature of the pedicellariae and spines, both plain 

 and striped fibres, consists of metamorphosed connective tissue cells. II. Ir re- 

 gular es. The phyllodean pedicels of the Spataugidae have a layer of con- 

 nective tissue and another of muscle fibres between the inner and outer epithelia. 

 The disc is hollow and divided by a number of perforated membranes into a series 

 of concentric spaces which communicate with the cavities of the capitate filaments 

 borne on the disc. The latter contain fine nerve fibrils which seem to terminate 

 in the cells of their epithelial covering, among which also amoeboid pigment cells 

 occur. The rosette-feet of the anterior ambulacrum have essentially the same 

 structure. The fascicles are remarkable for the great development of the inte- 

 gumental nerves ; the epithelium above them contains sensory cells and supporting 

 cells, the latter of which send processes downwards through the nerve that reach 

 the basal membrane beneath it. As in the Echinidae the radial nerve is situated 

 in a schizocoel space which it divides into two parts, and its outer face is covered 

 with protecting cells, which have, however, no inward supporting processes. All 

 the integumental nerves have an epithelial position and are separated from the 

 cutis by a basal membrane. The walls of the digestive tube contain bundles of 

 nerve fibres which are in direct connection with the oral ring and are in relation 

 both with the muscular fibres and with the inner epithelium of the gut. - The 

 vascular system of the Spatangidae differs somewhat from that of the other 

 Urchins. For the dorsal and ventral lacunar vessels of the digestive tube arise 

 directly from the schizocoel ring space around the mouth, and not from a distinct 

 blood lacunar ring. A water- tube, arising from the water-vascular ring, accom- 

 panies the dorsal vessel on the left side of the gullet. The former soon breaks up 

 into smaller cavities which communicate both with one another and with that of 



