ECHINODERMS. 135 
are situated pear-shaped vesicles, collected in some species into 
bunches, which TIEDEMANN conceives to be male genital organs, 
an opinion which falls to the ground now that the sexes are known 
to be distinct. Moreover they do not lead into this canal, but are 
in connexion with the cesophagus. It must be noted as a remark- 
able exception that in Synapta, according to the investigations of 
QUATREFAGES, a complete hermaphroditism prevails. The genital 
organs have the form of long strings, whose internal surface is beset 
with conical structures containing Spermatozoa, whilst the inner- 
most cavity is filled with a pulpy substance in which the eggs are 
found. ‘These eggs, as they grow, are pressed against the conical 
structures and so fertilized; and then the germ-spot, which was 
before visible, disappears. As the development of the eggs pro- 
ceeds, the testes which adhered to the inner wall of the string and 
surrounded the eggs, are so much compressed that they become 
atrophied and disappear. This periodical development is a very 
remarkable physiological phenomenon !. 
With the exception of some interesting observations of SARs 
little was known respecting the development of Echinoderms until 
the last few years. [To the distinguished and unremitted labours of 
MUELLER we are principally indebted for nearly complete informa- 
tion respecting the very curious and unexpected processes which 
occur in different species. Very remarkable differences are observed 
according as more or less of the development is effected within the 
body of the parent, or according to the locality where the embryo 
is deposited on leaving the egg, or according to the different modes 
in which it is destined to acquire its food. As a general rule it 
may be stated that in littoral species when the embryo escapes at 
an early period from the egg the series of metamorphoses is less 
numerous: but that in pelagic species, where the embryo has to 
seek its food by swimming on the surface, the necessity for provi- 
sional organs of a complicated nature renders the changes very 
1 Ann. des se. nat., sec. sér, XVII. 1842. Zool. pp. 66, 73. A talented observer, whom 
we have already quoted when treating of Polyps, (p. 70.) STEENSTRUP has with much 
acuteness endeavoured to reject Hermaphroditism altogether, and is of opinion, that 
even here QUATREFAGES has taken cells of spermatozoa for eggs without the germinal 
spot. Undersoegelser over Hermaphroditismus Tilvaerelse i Naturen, Kjobenhayn, 
1845, 4to, pp. 63, 64. (SIEBOLD also surmises the same mistake of QUATREFAGES.) We 
shall perhaps recur subsequently to STEENSTRUP’S opinion. 
