35 



cancriformis : other Nanplii and Amymonce are entered among the synonyms of the full- 

 grown parents to which they severally belong — as, e.g., to Canthocamptus minufus, Baird, 

 C. stroma, C.furcatus, C. chelifer, &c. The ' NaupUus' oiBalanus, i. c. the yo\xng of that 

 Barnacle after quitting the q^^^, is a free ' hexapod,' Avith relatively larger swimming- 

 limbs, furnished with more numerous and relatively longer sctyc than in N. saUator'ms *. 



Kg. 9. 



Fig. 10. 



Nauplius saltatorius (j'oung of Cyclops). 

 (After Eaird, op. cit. tab. xxiv. fig. 9.) 

 Naitplius (young of Apxis) cancriformis, 

 (After Baird, op. cit. tab. i. fig. 2.) 



Thus it appears that Naupl'ms is not a ' thing ' but a ' name.' That is, the term 

 means not one but many things, and all of them known more truly or scientifically under 

 other * nomina ' of multitude, both generic and specific. 



It is essential in this part of my memoir to hold an intelligible idea of what is signified 

 by NmipUns, in reference to its application to the question whether the embryonal de- 

 velopment of Limuliis is a " recapitulation of the history of all its ancestors," or merely 

 a manifestation of the phases of its own specific growth — and if the latter, whether any 

 of those phases resemble not a Naupl'ms only, but other species or genera of Crustacea, 

 more, and in more essential characters, than they resemble later phases or the generic 

 characters of the parent. 



At the phase of development of Limulus (fig. 4) which is called the ' Nauplius stage ' t, 

 the resemblance is as follows : the limbs are restricted to the part of an undivided 

 body answering to the later-defined ccphaletral division, as yet not distinctly marked 

 out. The correspondence of the embryo Limulus to the young Entomostracan is 

 carried no further. The cephaletral limbs in the former are mere buds ; the terminal 

 joint is bent on the proximal one ; there is no trace of setao, not the slightest indication 

 of any transitional natatory structure or function of such embryonal limbs. The mouth 

 opens, almost, in its limulino relations to the antennules (ii) and antennae (iii) ; and 

 these already show their characteristic difference of size. Their next step is to gain the 

 prehensile chelate structure, as in the adult. What tlie "famous Nauplius" maybe 

 I have not been able to make out ; but if the stage in question really represents any 

 " common ancestor," it certainly is not the Nauplius of carcinologists. It may also be 

 remembered that Lmmlus differs from the parents of Nauplil, i. c. Copcpods, Phyllopods, 

 and other Nauplian Entomostraca, in the eggs being left to hatch in a sand nest, not 

 carried about in egg-bags. 



* C. Spcncc Bate, " On the Development of tlic Cirripcdia," in ' Annals and Magazine of Natural History,' rind 

 Scries, vol. viii. (1851) p. 324, pi. vi. fig. 1, Baluuus bidunoli.les ; fig. 5, Bahinus ptrforutas. 

 t Packard, he. cii. pp. 1G3, 202. 



p2 



