58 SUMMARY OF CURRENT RESEARCHES RELATING TO 



sinus (perihrcmal of Ludwig and Koehler, to which alone tho term is 

 applicable), and then tho ambulacra! canal. The vascular ring is con- 

 nected to the aboral by a sinus which incloses tho ovoid gland and the 

 sand-canal ; the aboral ring gives off the genital vessels which form a 

 blooil-sinus around the genital cajca ; in the interior of the aboral ring 

 and its appendages there is, as in Asterids, a genital cord, at the expense 

 of which the genital organs are formed ; this, in the adult, becomes 

 fused with tho base of each genital organ. It incloses a certain number 

 of nuclei and of cells which are similar to those of the ovoid gland ; in 

 addition there are cells of large size, with a large nucleolated nucleus, 

 which are identical with young ova and the mother-cells of sj)ermatozoa ; 

 where the genital cord is in contact with the genital ca3ca the cord is 

 composed solely of these cells. 



The lymj)hatic glands are, partly, the Polian vesicles for the arnbu- 

 lacral apparatus, as in Asterids and Holothurians, partly the ovoid gland 

 for the vascular apparatus and general cavity, and, partly, the small 

 glands which are placed at the outer extremity of the respiratory cleft ; 

 the products of these last are probably destined for the genital vascular 

 apparatus. 



Development of Apical Plates in Amphiura squamata.* — Dr. P. H. 

 Carpenter takes as his text Mr. J. W. Fewkes's recent observations on 

 the development of the calcareous plates of Amphiura squamata. He 

 urges that the radial plates are mutually homologous in Ophiurids and 

 Urchins, Asterids and Crinoids, and that the relative time of their 

 appearance is of no general morphological importance. As against 

 Fewkes's view that the radial shields of Amphiura are the homologues 

 of the first brachials of a Crinoid, three objections are raised. Many 

 Crinoids have no paired first brachials, for they have only five arms ; 

 the only genera in which the paired first brachials rest directly on the 

 primary radials are the aberrant AUagecrinus and Tribachiocrinus, but 

 this is not the case all round the cup ; the radial shields are often 

 separated from the primaries by a series of intermediate plates, which 

 exhibit no general constancy of arrangement. Dr. Carpenter would 

 prefer to regard the radial shields of Ophiurids as being, like the 

 terminals of both Ophiurids and Asterids, without representatives in 

 the Crinoidea. 



In defence of his homologization of certain intraradial plates in 

 Amphiura with the basals of Crinoids the author points out that the 

 plates in question have an interradial position within the ring of 

 radials, and are at one sto.ge of development the only adaxial interradial 

 plates ; so that they correspond exactly to the basals of monocyclic 

 Crinoids and to the so-called genitals of Urchins and Asterids. 



Attention is particularly directed to the considerable difference in 

 the order of formation of the principal apical plates in the American 

 and European varieties of the same species ; though this does not seem 

 to have attracted the special notice of Mr. Fetvkes, it bears very strongly 

 on any argument as to homology which can be extracted from differences 

 in the time of appearance of plates. 



Calcareous Corpuscles of Holothurians.f — M. E. Herouard has 

 examined the calcareous deposits of a number of dendrochirotous Holo- 



* Quart. Journ. Micr. BcL, xxviii. (1887) pp. 303-17. 

 t Comptes Rendus, cv. (1887) pp. 875-ti. 



