‘SEPTEMBER 25, 1902] 
NATURE 
527 
*«Naples Zoological Station,” and others which might be 
aamed ; while in the discovery and successful monographing, 
in the intervals of six years’ labour at other groups, of a new 
family of minute Copepods (the Choniostomatidze), parasitic on 
the Malacostraca, embracing forty-three species, difficult to find, 
we have an almost unique achievement. The hand which gave 
us this has also provided a report which embraces the descrip- 
tion of a nauplius of exceptional type, which, by a process of 
reasoning by elimination, masterly in its method, has been “ run 
to ground ” asin every degree of probability the larva of Darwin’s 
apodal barnacle Profolepas bivincta, of which only the original 
specimen is known. 
There is but one other crustacean record equal in rank with 
this, viz., the discovery of the genus Anaspides. Originally 
obtained from a fresh-water pool on Mount Wellington, Tas- 
mania, at 4000 feet, it has since been found in two other locali- 
ties. It is unique among all living forms, in combining within 
itself characters of at least three distinct suborders of ‘‘ prawns,” 
for with a schizopod body it combines the double epipodial 
lamellze of an amphipod, the head of a decapod (pedunculated 
eyes and antennulary statocysts) apart from characters peculiarly 
its own. There is reason to believe that the nearest living 
ally to this remarkable creature is a small eyeless species (Lathy- 
nella natana) obtained from a Bohemian well ; and if its pre- 
sumed relationships to the Paleozoic ‘‘ pod-shrimps” be correct, 
this heterogeneous assemblage may perhaps be the representatives 
of a group of primitive Malacostraca, through which, by structural 
divergence, the establishment of the higher crustacean suborders 
may have come about. 
It is pertinent to this to note that work upon cave-dwelling 
and terrestrial forms, upon ‘‘ well-shrimps” and the like, has 
produced important results. And interesting indeed is the 
recent discovery of three species. living at 800-900 feet above 
sea-level, in Gippsland, one an amphipod, two of them isopods, 
which, though surface-dwellers, are all blind. While they prove 
to be species of genera normally eyed, they in their characters 
agree with well-known American forms; and the bleaching of 
their bodies and atrophy of their eyes proclaim them the de- 
scendants of cave-dwelling or subterranean ancestors, among 
whom the atrophy took place. 
Huxley in 1880 rationalised our treatment of the higher 
Crustacea, by devising a classification by gills, expressive of 
the relationships of these to the limb-bases, interarticular mem- 
branes and body-wall. Hardly had his influence taken effect 
when, by work extending over the years 1886 to 1893, in the 
study of Penzeus, the Phyllopods, Ostracods and other forms, 
evidence had been accumulating to show that the crustacean 
appendage, even to the mandible itself, has primarily a basal 
constituent (protopodite) of three segments; that the branchize 
one and all are originally appendicular in origin ; and that the 
numerical reduction of the basal (protopoditic) segments to two, 
with the assumption of a non-appendicular relationship by the 
gills, is due to coalescence of parts, with or without suppression. 
The evidence for this epoch-making conclusion, which simplifies 
our conceptions and brings contradictory data into line, is as 
irresistible as it is important, and there has been nothing finer 
in the whole history of crustacean morphology. With it, the 
attempt to explain the supposed anomalous characters of the 
antennule by appeal to embryology goes to the wall; and, 
taking a deep breath, we view the Crustacea in a new light. 
There remains for brief consideration one carcinological dis- 
covery second to none which bears on the significance of larval 
forms. It is that of the Trilobite 77zarthrus Beckz, obtained in 
abundance from the Lower Silurian near New York, with all its 
limbs preserved. In the simplicity of its segmentation and the 
biramous condition of its limbs it is primitive toa degree. Chief 
among its characters are the total absence of jaws in the strict 
sense of the term, and the fact that of its three anterior pairs of 
appendages the third is certainly and the second is apparently 
biramous, the first uniramous and antenniform. In this we 
have a combination of characters known only in the nauplius 
Jarva‘among all living crustacean forms; and the conclusion that 
the adult trilobite, like that of the Euphausiacez, Sergestidze, 
Penzidz, the Ostracods and Cirripedes of to-day, was derived 
by direct expansion of the nauplius larva can hardly be doubted. 
Much yet remains to be done with the study of the Triarthrus 
limbs ; and the suggestion of a foliaceous condition by those of 
the pygidium, which are youngest, is a remarkable fact, the 
meaning of which the future must decide. We should expect 
the condition to be a provisional one, since while we admit the 
NO. 1717, VOL. 66] 
primitive nature of the phyllopods as an Order, we cannot 
regard the foliation of their appendages as anything but a 
specialisation. Be this as it may, the structural community 
between the nauplius larva and the trilobite is now proved ; and 
when we add that in the yolk-bearing higher Crustacean types 
(e.g. Astacus) a perceptible halt in the development may be 
observed at the three-limb-bearing stage; that in Mysis the 
vitelline membrane is shed but to make way for a nauplius 
cuticle ; and that the median nauplius eye has long been found 
sessile on the adult brain of representative members of the higher 
crustacean groups, up to the lobster itself, our belief in the 
ancestral significance of the nauplius larval form is established 
beyond doubt. 
The thought of the nauplius suggests other larval forms. The 
gastrula is no longer accepted without reserve; the claims of 
the blastula, planula, parenchymella, not to say the plakula, 
have all to be borne in mind. It is of the Trochophore, how- 
ever, as familiar as the nauplius, that I would rather speak, as 
influenced by recent research. It is supposed to be primitive 
for the molluscs and chetopod worms at least; and various 
attempts have been made to bolster it up, and to show that if 
we allow for adaptive change, its characters, well known, are 
constant within the limits of its simpler forms. 
It is now more than forty years ago that the late Lacaze- 
Duthiers described for Dentalium a larval stage, characterised 
by the possession of recurrently ciliated zones, which by reduc- 
tion, with union and translocation forwards, give rise to the 
trochal lobe. It is now known that in the American pelecypod 
Voldia limatiula a similar stage is found, in which a ‘‘ test,” of 
five rows of ciliated cells, is present ; and of the young of 
Dondersta banyulensis the like is true. But whereas in the 
Yoldia the ciliated sac is ultimately shed, in the Myzomenian 
the escape of the embryo is accompanied by rupture which 
liberates the anterior series of ciliated zones in a manner strongly 
suggestive of forward concentration, leaving the posterior circlet 
with its cilia attached. 
This ‘‘ test’ has also been seen in two species of Nucula, and 
pending fuller inquiry into the Myzomenian and a reinves- 
tigation of Dentalium, I would suggest that this recurrently 
ciliated sac is representative of a larval stage antecedent to the 
trochophore, for which the term fvotvocha/ may suffice. This 
term has indeed been already applied to a larva of certain Poly- 
cheeta, which might well represent a modification of that for 
which I am arguing ; and quite recently it appears to have been 
observed near Ceylon for a species of the genus Marphysa. 
The discovery of this larva in Dondersia was accompanied by 
that of a later-formed series of dorsal spicular plates, which for 
once and for all, in realising a chitonid stage, demolish the heresy 
of the ‘‘Solenogastres,” mischievous as suggesting an affinity 
with the worms. Like that of the supposed cephalopod affinities 
of the so-called ‘‘ Pteropods,”’ it must be ignored as an error of 
the past. 
Returning to the protrochal stage, whatever the future may 
reveal concerning it, by bringing together the Lamellibranchiata, 
Scaphopoda and Polyplacophora, it associates in one natural 
series all the bilaterally symmetrical Mollusca except the cephal- 
opods. In doing this, it deals the death-blow to the supposed 
Rhipidoglossan affinity of the Lamellibranchiata; and in sup- 
port of this conclusion I would point out that the recently dis- 
covered eyes of the mytilids are in the position of those of the 
embryo Chiton, and that just as Dentalium, in the formation 
of its mantle, passes through a lamellibranchiate stage, so are 
there lamellibranchs in number in which a tubular investment is 
found. 
This protrochal larva has an important part to play. It may 
very possibly explain phenomena such as the compound nature 
of the trochal lobe of the limpet, the presence of a post-oral 
ciliated band in the larva of the ship-worm, and of a pree-anal 
one in that of various molluscan forms. In view of it, we must 
hesitate before we fully accept the belief in the ancestral signi- 
ficance of the trochophore. And it is certain that an idea, at 
one time entertained, that the Rotifer (Trochosphzra) which so 
closely resembles it as to bear its name is its persistent repre- 
sentative is wrong, since this is now known to be but the 
female of a species having a very ordinary male. 
Through the Rhipidoglossa we pass to the Gastropods, which 
are one and all asymmetrical, for even Fissurella, Patella and 
Doris, when young, develop a spiral shell ; while Huxley in 
1877 had observed that the shell of Aplysia, in its asymmetry, 
betrays its spiral source. 
