690 DE. W. B. CARPENTEE OX THE STEUCTUEE, PHYSIOLOGY, AXD 



ova in the swollen portions of the pinnte has been seen not merely by Mr. J. V. Tnoiirsox, 

 but by M. Dl-jardix, Professor Mullee, Dr. Buscii, Professor Wyville Thomson, and 

 myself. The fact is that these animals are unisexual ; and that while ova are produced 

 in the conceptacles of some individuals, spermatozoa are developed within others, and 

 are set free in the same mode. 



The statement of Mr. J. V. TliOMPSOX as to the identity of his Penfaciinus with the 

 5^oung of Comatida, on which doubts had been cast by M. Dujakdin', was satisfactorily 

 confirmed by Professor Forbes. " When dredging in Dublin Bay," he says (Introduction, 

 p. xii), "in August 1840, with my friends Mr. R. Ball and AV. Thompson, Ave found 

 numbers of the Phytocrinus or Polype-state of the Feather-star, more advanced than 

 they had ever been seen before, so advanced that aac saw the creature drop from its stem 

 and swim about a true Comatula ; nor could Ave find any difference betAVcen it and the 

 perfect animal, Avhen examining it under the microscope." He did not, however, add 

 anything to the account previously given by Mr. J. V. Thojipson of the successive stages 

 of development of this Pentacrinoid larva ; and his description of the structure of its 

 calcareous stem is very far from being accurate, as I shall have occasion to shoAv here- 

 after. 



The remarkable discoveries of Professor Muller and other observers in regard to the 

 larval or pro-embryonic forms of Echinida, Asteriada, and Ophiurida, naturally led to 

 the suspicion that some corresponding form of free-swimming pro-embryo must be the 

 first product of the egg of Antedon ; and that this probably gives origin to the Pentacri- 

 noid larA'a by a process somcAvhat similar to that by Avhich the young Uch'nus originates 

 from its " pluteus," or the Asterias from its " bipimiaria." To the solution of this pro- 

 blem Dr. Wile. Busch% a pupil of Professor Muller, applied himself in 1849 ; and he 

 Avas fortunate enough to discoA'er such a free-SAvimming pseudembryo, somcAvhat Anuelidan 

 in its form ; though he did not succeed in tracing it beyond its earliest stages, or in 

 shoAA'ing hoAV the Pentacrinoid larva originates from it. It is probably through not 

 having done so, that his interpretation of his observations AA^as in many points incorrect ; 

 as has been shoAvn by the more recent and complete researches of Professor Wyville 

 Thomson^, Avho has Avorked out this part of the developmental history of yintedon Avith 

 a completeness that leaves scarcely anything to desire, and Avho (in accordance AAdth my 

 request) has not only traced the metamorphosis of the frce-SAvimming pseudembryo into 

 the pedunculate Crinoid, but has carried on the description of the latter to the stage at 

 Avhich my oaau observations best enable me to take it up. 



In 1856 an account was published by Professor Sars of the Pentacrinoid stage of 

 Antedon Sarsii; but as the prmcipal points of interest in this communication have 

 already been noticed in Professor Wyville Thomson's Memoir (p. 516), I need not 



1 L'lustitut, No. 119 (1835). 



- " Ccber die Larvc der Comatula,'' in Miiller's Arehiv, 1S49, p. 400; and iu BeobacMungen iiber Anatomic 

 und Entwiekelung oiniger wirbellosen Seethierc. Berlin, 1851. 



^ " On the Embi-jogeny of Antedon rosaceit^," in Pliilosophical Transactions for 1865, p. 513. 



