V. Echinoidea. \ \ 



beneath which is a triangular depression lodging a process of the gland and its 

 extensions into the spongy tissue near the anus. The materials reaching the 

 gland by the vascular plexus above mentioned are here elaborated into the cellu- 

 lar elements found in the coelom and elsewhere. 



Prouho ( 3 ) finds that the ovoid gland of Spatangus, like that of Dorocidaris, 

 has a glandular process which is in relation with much spongy tissue and lies 

 between the 2 plates of the supporting apparatus beneath the madreporite. The 

 duct of the gland and the water-tube open externally at the hinder end of the right 

 hand plate. The middle part of the water-tube, alongside the gland, loses its 

 columnar epithelium and becomes an irregular channel with lateral ramifications, 

 some of which extend over the blood vessel that connects the oral blood- vascular 

 ring with the ovoid gland. The 2 structures together form a sort of double canal 

 which reaches from the ovoid gland to the 2 oral rings. This, the canal du 

 sable of authors, is homologous with the Polian ring of the Cidaridae, and may 

 be called the Polian canal, each half being connected with an oral ring and 

 radial vessels. 



Kbhler (*) admits that he was wrong in denying the existence of pharyngeal 

 vessels in the regular Echinids [see Bericht for 1885 I p 191]. He confirms 

 Proilho's ( 2 ) rediscovery of them in Dorocidaris and also finds them in Echinus, 

 Sphaerechinus and Strongylocentrotus. But he regards the composite Polian canal 

 of Spatangus as homologous in the regular Urchins with the water-tube (stone- 

 canal) and the glandular canal together. It is not represented by the composite 

 Polian ring of the Cidaridae as stated by Prouho ( 3 ), for this consists of two oral 

 rings, homologous with those of Echinus and Spatangus. But in all the Urchins 

 alike the 2 vascular systems are intimately related either at the level of the oral 

 rings (Regulares) or between them and the ovoid gland (Irregulares). Prouho ( 4 ) 

 comments on Kohler s (*) treatment of his observations. 



Vogt & Yung's account of the anatomy of the Urchins is largely based on 

 the works of Perrier and Kohler [see Bericht for 1883 I p 130]; but they do not 

 find the dorsal organ to communicate with the exterior through the madre- 

 porite by means of an excretory duct, as stated by these authors. Its upper end 

 is connected , beneath the madreporite , with a pentagonal ring that unites the 

 5 genital ducts , and contains lacunae with cells like those of the dorsal organ. 

 It is homologous with the genital cords of Comatulae. The ventral end of the 

 dorsal organ is connected with the second oral ring as described by Kohler, but 

 only one set of radial vessels could be clearly distinguished. The water- vascular 

 and irrigation systems communicate by means of the so-called Polian vesicles and 

 the sub-madreporic ampulla. 



Beddard notes the existence of striated muscles in the pedicellariae of 

 various species of Echinids. - - Duncan regards the organs described by Hamann 

 as Globifereu as pedicellariae especially modified for the secretion of mucus ; for 

 they contain atrophied calcareous valves. 



The cousins Sarasin describe an Echinothurid with poison-sacs at the ends 

 of its spines, and 5 pairs of longitudinal muscles which depress the test. Among 

 the spines a fish and a Decapod were living commensally. 



Duncan & Sladen find that each of the basals of Discoidea cylindrica is per- 

 forated for the madreporite, but that the fifth has no genital opening; and 

 they describe the variations in the characters of the poriferous zones during the 

 growth of the test. There is a continuous p e r i g n a t h i c g i r d 1 e , the interradial 

 and larger portions of which represent the ridges of the other regular Echinids 

 [see Bericht forl885Ip!90]. The radial portions of the girdle are perforated by 

 tentacular pores and represent the processes of the ambulacral arches in Echinidae. 



