13 



pound Radiaries would seem, rather than the oviparous 

 medusiform ones, to manifest the typical form of the spe- 

 cies ; as the leaf is a more typical form of the plant than 

 the parts of the flower; and as the free-swimming Cirri- 

 pedal larva, with its pedunculated eyes, is more typical of 

 its class than is the blind and fettered multivalve Barnacle 

 into which it is so marvellously transformed. Superadd, 

 however, distinct nutritive and circulating organs to the 

 free-moving ovigerous individual from the rooted polype, 

 and prolong its existence, and it would then cease to have 

 the ancillary character of a nurse to the ova of the fixed 

 individuals, and would assume that of the perfected form 

 of the species, and such in fact is the case with the larger 

 gelatinous Radiaries called Medusa. 



The egg of the species called Cyancea aurita is devoid of 

 a chorion*, and consists, after impregnation, of the germ- 

 mass only, formed according to the before-defined process 

 for the dissemination of the spermatic principle f. By the 

 combination and metamorphosis of the peripheral series of 

 secondary germ-cells a ciliated epithelium is formed J : an 

 assimilative cavity results from the liquefaction of certain 

 central germ-cells : the germ-mass grows, elongates, and is 



* Siebold, Beitrage zur Naturgeschichte der Wirbellosen Thiere, 4to, 

 1839, p. 21. 



f The external signs of these universal preliminary steps in develop- 

 ment ab ovo are figured in the above-cited work, in tab. 1. figs. 1-13. 

 The preliminary internal changes may be inferred from what was ob- 

 served by Siebold and Bagge in the ova of the Strongylus auricularis (De 

 Evolutione Strongyli, 4to, 1841), some of whose figures are copied in my 

 'Lectures on the Invertebrata/ 8vo, 1843, p. 77, figs. 33-44, where I 

 remark, as Dr. Martin Barry had, also, independently remarked (see 

 the note which he communicated to the same work) : "This prelimi- 

 nary division of the clear central cell to the spontaneous fission of the 

 yelk is closely analogous to that division of the central cell in the poly- 

 gastrian animalcule, preparatory to the spontaneous division of its body 

 into two individuals, which Ehrenberg described." (See PI. I. figs. 

 4 13 of the present ' Discourse/) 



J Siebold, loc. tit. fig. 19. Ib. fig. 15. 



