14 Echino derma. 



where it bears the lower end of the ovoid gland. This consists of a connective 

 tissue basis forming areolae which lodge the pigineuted amoeboid cells. These 

 are formed in the gland and escape from its meshes into the axial sinus around 

 it which is in connection below with the oral blood sinus. The upper end is 

 attached round the madreporite, beneath which it gives off a spacious internal 

 ampulla separated from it by a membranous septum. The dorsal end of the ovoid 

 gland pierces this septum and is attached to the opposite wall of the ampulla. It 

 contains amoeboid cells but little pigment. Before reaching this ampulla the ovoid 

 gland gives off a process which pierces the wall of the axial sinus and hangs freely 

 into the coelom as its lymphatic gland. It is not, as often described, a vascular 

 apparatus proceeding to the stomach. Some of the pore canals of the madreporite 

 lead into the axial sinus ; while in Asterina gibbosa and E. sepositus the terminal 

 ampulla of the axial sinus also communicates with the exterior through the madre- 

 porite. [Compare Hamann in Bericht for 1SS5 I p 189.] An important part of 

 the blood-system is that in relation with the genital organs. The axial sinus 

 terminates dorsally in a pentagonal sinus lined by pavement epithelium which 

 gives off 2 vessels at each interradial angle. The sinus contains a pentagonal 

 genital cord of the same structure as the ovoid gland which it joins, and it sends 

 an extension into each genital vessel. Lateral branches of each cord develope 

 into genital caeca and acquire external openings, while the central cord within 

 the pentagonal sinus becomes the lymphatic gland of the genital system, producing 

 amoeboid cells which escape into the sinus around it. In some species its 10 inter- 

 radial branches acquire the same character. The lymphatic globules absorb al- 

 buminoids which are utilised by the genital organs. Both the pentagonal sinus 

 and the genital vessels are well defined regular cavities lined by a vibratile epi- 

 thelium, and not mere interstitial lacunae in the connective tissue (schizocoel) . All 

 these blood-sinuses and vessels are merely extensions of the coelom and their con- 

 tents are moved by the cilia of the vibratile epithelium, though not in any definite 

 direction. When the vertical septum in the radial sinus is thick as in Asterias, it 

 is not pierced by a longitudinal blood-vessel as described by Ludwig, but consists 

 of alveoli enclosing amoeboid cells, and represents the lymphatic gland of the ray. 

 These cavities, however, are obliterated with age and do not extend into the septum 

 traversing the oral blood-sinus, on which the ovoid gland rests. The vascular 

 system of the Asteriadae thus consists of 3 parts, each containing a lymphatic 

 gland, but only in restricted communication with one another: 1) the radial 

 sinuses and the outer part of the oral sinus which opens into the coelom; 2 1 the 

 inner part of the oral sinus and the axial sinus, which opens externally through 

 the madreporite; 3) the aboral sinus and its extensions round the genital organs. 

 The Echinasteridae and Linckiadae have no radial lymphatic spaces, and all the 

 blood-sinuses communicate freely. In Gymnasteria the radial septum is calcareous 

 and nearly fills up the sinus; and it is not perforate either in Astropccten or in 

 Asterina. The external genital openings always occupy the positions of the 

 papulae; so that they occur singly in Astropectiuidae, Culcitidae, Asterinidae, 

 and Echinasteridae, but are grouped together in the Asteriadae, A. glacialis having 

 from 3-9 in a group. The sexual glands are formed at the expense of the ge- 

 nital cords and the cells lining them are at first identical with lymphatic cells, 

 ovary and testis being indistinguishable. In the Q? As'ropectinidae a cavity ap- 

 pears in the centre of each genital cord and the cells immediately lining it give rise 

 to the spermatozooids the peripheral ones remaining as inactive lymphatic cells ; 

 while in other families the parietal cells become the sperinospheres and the cen- 

 tral ones are resorbed or discharged. The nucleus (with its nucleolus) of each 

 primordial cell undergoes repeated division to form a mass of nuclei imbedded in 



