Hyatt.] 398 [Nov. 16, 



groups as their existing adults. They do not possess, as a rule, 

 the essential diagnostic characters of the larger divisions to which 

 they belong, and we propose to call them Neoembryos. Examples : 

 the Cinctoplanula is not a sponge, the Planula of the Coelenterata 

 is not a Coalenterate, nor the Pluteus an Echinoderm, nor the Tro- 

 chosphere a Mollnsk, nor the Pilidium a Nemertean worm, nor the 

 earliest planula-like ciliated stages of Amphioxus a Vertebrate. 

 Neoembryos are, as pointed out by Semper, 5 Lankester 6 and Bal- 

 four 7 , so similar, that they may be considered as indicating a com- 

 mon ancestor for the entire Animal Kingdom. 



(7) The latest of the more specialized planula-like stages are 

 either directly transformed into, or else give rise to other forms in 

 which the characters of the larger subdivisions or types of the An- 

 imal Kingdom begin to appear, at least so far as essential charac- 

 ters are concerned. Examples: the Ascula and Ampullinula are 

 true sponges, the Actinula is a Hydrozoon, the Gulinula is an Ac- 

 tinozoon, the Veliger is a Mollusk, the internal worm-like form 

 arising in Pilidium is a true Nemertean, the formation of the no- 

 tochord in Amphioxus makes the planula-like embryo into a ver- 

 tebrate animal. They have the essential characters of the larger 

 subdivisions, though it is equally true, that embryos in this stage 

 of development are very remote, in some cases, from the adults 

 of any normal forms. We do not, therefore, misinterpret these 

 relations by naming the embryo in these last stages the Typem- 

 bryo. 8 This term can be applied to the Nauplius of Crustacea, 

 and the Echinula 9 of Echinodermata, as well as to those above noted. 



6 Semper, Stammsver. Wirbel. und Wirbellos., Arbeit. Zoolog. Zootom. Inst., II, 

 p. 59, and in, p. 384. This distinguished author states in Volume in, that his " Tro- 

 chosphaera" is identical with the " ungegliderte Urnierenthier," which in his first 

 table in Volume II, appeared as the common ancestor of the higher animals, i. e., of 

 all animals except Echinodermata and Coelenterata. 



6 Lankester traced the Mollusca, Annelida, Rotifera and Echinodermata to what 

 he calls the Architroch, a common form taken from somewhat earlier stages of the 

 Planula than those selected by Semper for his Trochosphaera, Embryol. and Classif., 

 Journ. Micros. Sci., XVII, 1877, p. 423. 



i Balfour, Comp. Embryol., II, p. 311. 



8 From *Tu7tos, type aiid*EM/3Cov, embryo. 



9 Alexander Agassiz, Address, Am. Ass. Adv. Sci., xxiv, 18S0, p. 410, shows that 

 there is a stage of the embryo common to all orders of living Echinodermata. This 

 stage, however, was not named in the address above quoted, which was intended as 

 preliminary to an illustrated essay on the same subject, and Mr. Agassiz has supplied 

 that omission in the following note, which I quote from a letter to me. "I intended 

 sometime when revising my 'Address on Palaeontological and Embryological Devel- 

 opment,' to call the earliest common stage of echinoderm embryos, 'Echinula' for 

 convenience in making comparisons. — A. Agassiz." 



