V. Echinoidea. 9 



bulacrals. Carpenter's views are accepted as regards the plates homologous with 

 the under-basals of Crinoids ; but the plates considered by him as basals may be 

 only interradials. The radial shields of Ophiurids are perhaps homologous with 

 the first brachials of Crmoids. Carpenter ( 4 ) criticises Fewkes' objections to re- 

 cognizing the presence of true Crinoidal basals in A. squamata, and reaffirms his 

 position. Fewkes' suggestion respecting the homology of the radial shields is 

 opposed for various reasons; and attention is directed to apparent differences in 

 the sequence of development of the apical plates in the American and Mediter- 

 ranean varieties. 



V. Echinoidea. 



See also Hamann (','), supra, p 3, Hartog, supra, p 4, and Kohler, supra, p 4. 



Haacke seeks to prove that the Urchins are radiate rather than bilateral ani- 

 mals. The missing paramer in tetra-radiate individuals is not always the same; 

 the ambulacral peristomial plates in a hex-radiate example are grouped symmetri- 

 cally ; the median plane is not always that of ambulacrum III (Loven) , and may 

 take at least 4 different positions when any paramer is hypertrophied. Eight 

 examples of Amblypneustes were found to have an additional madreporite which 

 was always situated between ambulacra III and IV. 



Hamann (*) has made a minute study of the anatomy and histology of the Ur- 

 chins. I. Regu lares. He adds somewhat to the descriptions of gemmiform 

 pedicellariae of Sphaerechinus given by Sladen and Foettinger [see Bericht for 

 1880 I p 267 ; 1881 I p 215]. The stem contains numerous nerves, partly in the 

 centre and partly beneath the basal membrane of the epithelium; they supply 

 both flexor and adductor muscles and the tactile cushion. The double glandular 

 sacs of the head open at the apex of each valve, as described by Sladen, and their 

 ducts are lined by a firm refractile chitin-like substance. Stem-glands are absent 

 in Echinus acutus, but the nerves are remarkably developed , as there is a second 

 tactile cushion near the apex of each valve, and an additional sense-organ in the 

 epithelium between it and the lower cushion. The tridactyle pedicellariae of Cen- 

 trostephanus longispinus have no glands and no definite sense-organs, but the ciliated 

 epithelium lining the upper portion of each valve contains cylinder cells and 

 sensory cells which receive branches from three nerves in the stem. The upper 

 part of the latter is occupied by an elastic ligament , owing to the shortness of its 

 calcareous rod, and the head is therefore more moveable than usual. The tridac- 

 tyle pedicellariae on the buccal membrane of Dorocidaris papillata have glands in 

 their valves. The opening of the valves of the pedicellariae is effected by extensor 

 muscles which are attached to the outer surfaces of the calcareous plates near 

 their bases. The movements of the head are produced by flexor muscles running 

 between the plates and the lime-stone rod of the stem. The pedicellariae in gene- 

 ral are tactile organs , the smallest or trifoliate ones clearing the test of minute 

 foreign bodies as described by Agassiz. The tridactyle ped. serve for the attach- 

 ment of the test, as seen by Romanes & Ewart, and also for removing larger 

 bodies from it; while the gemmiform ped. assist in the latter process by dischar- 

 ging mucus, as described by Sladen. - - Under the name glob if eri he describes 

 certain organs in Sphaerechinus granularis and C. longispinus which had not been 

 previously recognised. They must not be confounded with the pedicellariae glo- 

 biferae of 0. F. Mitller and later authors (gemmiformes, Hamann). Each consists 

 of a short stalk supporting three great mucus-glands , which are united at their 

 bases but free above, where they open externally. They are lined by long cylin- 

 drical cells, the outer portions of which seem to be destroyed in producing the mu- 



