G90 DE. W. B. CAEPENTEE ON THE STEUCTUEE, PHYSIOLOGY, AXD 



ova in the swollen portions of the pinna; has heen seen not merely by !Mr. J. V. Thomi'SON, 

 but by M. DuJARDJN, Professor MUllek, Dr. Buscii, Professor Wyvillk 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. Thompsox as to the identity of his Pentacrinus with the 

 young of Comatula, 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. E. Ball and W.Thompson, we found 

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

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

 and swim about a true Comatula ; nor could we find any difference between it and the 

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

 anything to the account previously given by Mr. J. V. Thompson 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 1 shall have occasion to show 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 larva by a process somewhat similar to that by which the young Uchinus originates 

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

 blem Dr. WiLH. BuscH^ a pupil of Professor MtJLLER, applied himself in 1849 ; and he 

 was fortunate enough to discover such a free-swimming pseudembryo, somewhat Annelidan 

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

 showing how the Pentacrinoid larva originates from it. It is probably through not 

 having done so, that his interpretation of his observations was in many points incorrect ; 

 as has been shown by the more recent and complete researches of Professor Wyyille 

 Thomson^, who has worked out this part of the developmental history oi Antedon with 

 a completeness that leaves scarcely anything to desire, and who (in accordance with my 

 request) has not only traced the metamorphosis of the free-swimming pseudembryo into 

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

 which my own 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 principal points of interest in this communication have 

 already been noticed in Professor Wyville Thomson's Memoir (p. 51G), I need not 



' L'lnstitut, No. 119 (1835). 



' "¥ebcr die Larve der Comatula," in MiiUcr's Archiv, 1849, p. 400; and in Beobachtungen iibcr Anatomie 

 und Entwickclung einigcr -wirbellosen Seethiere. Berlin, 1851. 



' " On the Embryogeny of Antedon rosaceus," in Philosophical Transactions for 1865, p. 513. 



