ZOOLOGY. 595 



starfishes and Opbiuroids, aud "regular with puhir difl'ereutiatiou " 

 iu the Ecbiuoids. " The various modes of eleavage are of no value for the 

 ph,vlogeuetic history of the group ; the iuflueuce of cenogeny is appar- 

 ent enough." For further and explanatory details the memoir of Pro- 

 fessor Selenka must be consulted, but his conclusions as to the genetic 

 relations of the group are of sufiicient general interest to warrant re- 

 peating here: " Evidence of the verniian origin of Echinoderms is af- 

 forded by the primary mesoderm having the form of two primitive cells 

 and by the bilateial symmetry of the larval organs. The division of the 

 archenteric diverticulum into codomic sac and water-vessels correspond 

 physiologically to that which the mesodermic sac undergoes in verte- 

 brates, and to some extent in worms." {^elenka's Studien iiber Entwicke- 

 lungsgescldclite, ii ; J. R. M. S. (2), iv, j)p. 573-574.) 



Crinoids. 



Reproductive function in Comatida. — interesting observations have re- 

 cently been made on the actions and apparent copulation of two indi- 

 viduals of the Comatula meditteranea by Dr. C. F. Jickeli. The phe- 

 nomenon resembled that previously noticed in a starfish {Asterina gib- 

 hosa) by Dr. H. Ludwig. The arms fell off as a climax, and this appeared 

 to confirm IStuder's sni)position that the loss of the arms, which often 

 occurs in star fishes, is ci)nnected with the discharge of the sexual pro- 

 ducts. {Zool. Anzeiger, Vii, pp. 444-^441) ; Ann. tt Mag. Nat, Hint. [6)^ 

 XIV, pp. 307-3(38; J. R. M. S. (2), y, pp. 70-71.) 



Asterioids. 



A deep-sea star-fish. — An interesting star-fish, obtained in Faeroe 

 Channel, at a depth of 555 fathoms, has been described by Mr. W. 

 Percy Sladen, under the name Mimaster Tizardi. Its interest arises from 

 the bonds of union with several quite diverse types, and it is indeed 

 what used to be called a synthetic or comi)rehen8ive type. It recalls 

 in different parts some Asteriidae {Solaster), Astropectinidie, Goniaster- 

 idiB, and Asteriuidae. It appears to he nearly related to a genus also 

 lately described, called Radiaster. {Trans. Royal Soc. Edinh., xxx, pp. 

 579-584, ] pi. ; J. R. M. S. (2), iv p. 903.) 



Echinoids. 



Morphology of the Echinoids. — In connection Avith studies of the Echi- 

 noids, and especially of the deep-sea species constituting the family 

 Pourtalesiidae, Prof. S. Loven has considered the general characters of 

 the order. Tlie skeleton is " a hollow sac inclosing the visceral organs, 

 and constituted by three distinct systems — ambulacral, ])erisomatic or 

 interradud. and calycinal or apical." On a careful study of this skeleton, 

 it is found mat "itsconstitueutelemcnts are in reality and fundamentally 

 arranged bilaterally and symmetrically on either side of the mesial 



