42 



SCIENCE. 



[Vol. XI. No. 260 



(6) The first and simpler planula stages, though often character- 

 istic of the larger divisions of the animal kingdom, do not possess, 

 as a rule, the essential, diagnostic characters of the larger divisions 

 to which they belong, and he proposed to call them ' neoembryos.' 

 Examples : the Cincioplanula, the planula of th,e Ccelenterata, the 

 Pluteus, the Trochosphere, the Pilidmm, the earliest planula-like 

 ciliated stages of Amphioxus. 



(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 divisions or types of the ani- 

 mal kingdom begin to appear, at least so far as essential characters 

 are concerned. Examples : the Asctila and Ampulliniila, the 

 Actinula, the Gulmtila, the Veliger, the internal worm-like form 

 arising in Pilidmm, the stage of the formation of the notochord in 

 Amphioxus. He proposed, therefore, to interpret these relations 

 by naming the embryo in these stages the ' typembryo.' This 

 term can be applied to the Natiplius of Crustacea, and the Echiii- 

 ula ' of Echinodermata, as well as to those above noted. 



The appUcation of such principles to the study of the younger 

 stages of fossil Cephalopoda was productive of what seemed to be 

 satisfactory results. The protoconch of Owen is, according to this 

 nomenclature, a shell of a univalve Veliger among the cephalous 

 Molbisca, and a typembryo, which, though eminently characteristic 

 of that group, has no exact morphological equivalent among nor- 

 mal adult forms of recent or fossil shells. 



The true larval, or, as they are here named, silphologic {'S'lXipJi, ' a 

 grub ') stages began with the formation of what Owen appropri- 

 ately called the apex of the conch or true shell. Among nautiloids 

 this was a short living chamber occupied by the body of the an- 

 imal, but having no siphon or septum. It was completed by the 

 deposition of the apical plate, which sealed up the aperture of the 

 protoconch, thus closing the opening, and cutting off communi- 

 cation between the two interiors. This stage can therefore be 

 named the ' asiphonula ' or siphonless larva. 



The second larval stage in Natitiloidea was composed of a liv- 

 ing chamber, closed apically and completed by a single septum, 

 which had a cascal prolongation reaching across the first air-cham- 

 ber and resting upon the inner side of the cicatrix. It is proposed 

 to call this stage the ' csecosiphonula,' since it is undoubtedly the 

 primitive stage of that organ. The cscosiphonula may indicate 

 the former existence of an ancestral form having a central axis 

 composed of similar closed funnels or caecal pouches. 



The third silphologic stage in nautiloids was completed by a sep- 

 tum (the second in the apical part of the shell) having an open 

 funnel extending apically and joined to a loose-textured siphonal 

 wall which reached down into and lined the caecum, thus forming 

 a secondary closed tube. In accordance with the structure, this 

 has been named the ' macrosiphonula.' 



The fourth larval stage of the nautiloids was completed by the 

 building of the third septum. This septum had a long funnel and 

 attached porous wall, but this wall formed a true siphonal tube 

 opening apically into the next section, the macrosiphon. This was 

 the beginning of the small siphon, and can be appropriately termed 

 the ' microsiphonula.' The microsiphonula was the typical stage 

 of nearly all the known genera of nautiloids, beginning with the 

 Orthoceratites of the Cambrian, and found at the present time in 

 Nautilus, and also of all ammonoids and belemnoids without ex- 

 ception. 



It has also been found in tracing the descent of forms within 

 sub-orders, families, and genera, that it is practicable to prove, 

 that characteristics usually appear first in adult stages, and are 

 then inherited at earlier and earlier stages in successive species • of 

 the same stock, whether they occur on the same horizon or in 

 different horizons. The adolescent stages are therefore of as great 

 importance for tracing the genealogy of small groups as are the 

 silphologic characters in larger groups. Thus one can speak in 

 definite terms of the relations of the nealogic {^takri^, 'youth- 



1 Address at the American Association by Alexander Agassiz, vol. xxix. 1880, p. 410 

 reprint, p. 22, shows that there is a stage of the embryo common to all orders of living 

 Ec7iinoderinata. 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 some time, when revising my ' Address on Paleontological 

 and Embryological Development,* to call the earliest common stage of echinoderm 

 embryos, ' Echinula,' for convenience in making comparisons. — A. Agassiz." 



fulness') stages, and Iheir meaning, and importance in tracing 

 the genealogy of families and genera, without danger of confusing 

 them with the characters of any of the silphologic stages. 



After the silphologic and nealogic stages have been disposed of, 

 there still remains the adult period, which is equally important in 

 genealogical investigations, since it enables the observer to study 

 the origin of many characters which afterwards become silphologic 

 and nealogic in descendant forms. 



The use of a distinct term for the adult period becomes neces- 

 sary not only on this account, and to separate its relations from 

 those of preceding periods, but also because of the constant recur- 

 rence and importance of representative forms. The term ' ephe- 

 bology ' ( ''Eip?/f)o;-, ' the age of puberty ') has accordingly been 

 adopted for the designation of the relations of the adult stages, and 

 under this term can be classified also the representation of similar 

 forms in different groups or morphological equivalents. These are 

 often so exact that it becomes very difficult to separate them. They 

 have been and will continue to be the most difficult and rhisleading 

 obstacles to the student of genealogy and classification. 



In former essays the senile transformations and their correlations 

 with the degraded forms of the same groups have been described 

 and defined by the term 'geratology ' (Tipa-, ' old age'). 



There were two stages of decline or old age among ammonoids. 

 The first of these is the clinologic (K'/.iva, ' to incline downwards') 

 stage. This immediately succeeded the ephebolic stage, and dur- 

 ing its continuance the nealogic and ephebolic characteristics un- 

 derwent retrogression. Ornaments, spines, and sutures degener- 

 ated and lost their angularity ; the ribs or pilse, and often the keel and 

 channels, when these were present, became less prominent ; and 

 before this period closed, the whorl itself sometimes decreased ; 

 showing that degeneration in the growth-force of the animal had 

 taken place. In man the baldness of the head, loss of teeth and 

 resorption of the alveoli, loss of the calves and rotund stomach, and 

 return of early mental peculiarities, are phenomena of similar im- 

 port. 



The last changes in the ontology of the animal took place in what 

 can be called the ' nostologic ' (Notr-or, ' a return ') stage, and during 

 this period these tendencies reached their highest expression. 

 Among ammonoids the ornaments were all lost by resorption, the 

 whorl became almost as round and smooth as it was in the silpho- 

 logic stage, and in extreme cases it even separated from the next 

 whorl, leaving a perceptible gap. This almost complete reversion 

 to the aspect of the silphologic stage can of course only occur in 

 animals which attain an extreme age. 



MENTAL SCIENCE. 



Aphasia.' 



In i86i Broca suggested before the French Society of Anthropol- 

 ogy that the only method of determining the functions of the brain 

 was to co-ordinate marked symptoms during life with the lesions 

 found in a post-mortem examination. Some months later he an- 

 nounced his belief that the third frontal convolution of the left 

 hemisphere of the brain was the seat of spoken language, and de- 

 scribed a case of a paiient called ' Tan ' because that was the only 

 word he used, helping himself out with various gestures. He had 

 no paralysis, and seemed to understand what was said to him. 

 The posterior half of the second and third left frontal convolutions 

 of the left hemisphere was the seat of the organic lesion. In the 

 same year a quite similar case of a man with only such scraps of 

 words as ' oui,' ' no,' etc., but with mental and motor powers intact, 

 showed in the autopsy a definite lesion in the third frontal 

 convolution of the left side of the brain. These remarkable 

 cases drew attention to diseases of this kind ; and in the end of 

 1863, eleven cases were on record in which the power of vocal 

 speech was almost or entirely lost, the common anatomical element 

 of each of which was a lesion in the posterior third of the third 

 frontal convolution of the left hemisphere. Broca called this condi- 

 tion ' aphemia,' and gave as its symptoms the loss of the power to 

 express ideas by vocal movements without any motor paralysis or 

 mental impairment. He concluded that memory was not a single 



1 Abstract of an address delivered before the Anthropological j Society at Paris by 

 M. Mathias Duval, Revue Scientijique, Dec. 17, 1887. 



