Dr. E. von Martens on the Species of Argonauta. 103 
It is an almost general rule throughout the animal kingdom 
that members of different species, genera, families, or orders 
agree more with each other in the first stage of their life than 
when full-grown; but very often this general resemblance is 
due rather to the special characters being indistinct, or not 
yet developed, not to the special similarity of them—as, for in- 
stance, the embryo of all the Vertebrata in its first period is 
similar, but not a fish or a bird, the distinctive characters of 
these making their appearance afterwards. In the present in- 
stance the sculpture, which is a rather special character, neither 
similar in all species of Trochus nor already formed within the 
egg, is specifically similar in the young state of both species; 
and the difference in the sculpture between the two full-grown 
shells arises not from any new character coming up, but from 
the disappearance, earlier or later, perfectly or partially, of that 
which has been common. If we may take for granted that 
the single species, such as they live at present, have not been 
created independently of each other, but that they are the 
descendants of others of other times, that. they bear the traces 
of their genealogy in themselves, and that the characters trans- 
mitted by a longer series of ancestors are also more constant 
and manifest themselves earlier in the youth of the individual, 
whereas the modifications acquired for the species in later times 
make their appearance less early in the course of individual 
development—if this be granted, then we may be entitled to 
pronounce that Trochus niloticus and Trochus maximus descend 
from similar, therefore probably common ancestors, which must 
have been sculptured throughout, with an even, spirally grooved 
base, such as is presented, for instance, among the now living 
allied species by 77. acutangulus,—that Tr. niloticus has deviated 
in the same space of time more from the common ancestors than 
Tr. maximus, the characters of the last whorl in 77. niloticus 
being quite new,—and that the above-mentioned premature spe- 
cimen of the same may give a hint as to the direction in which 
the species will change itself in future times. 
VI. On the Species of Argonauta. 
Linné comprises all the Argonaute known to him in one 
species, A. Argo; his second species, A. Cymbium, is a foramini- 
ferous shell (Peneroplis planatus, Montfort), as is proved by his 
own words, “testa vix minime arenule magnitudine,” and by 
the quotation of Gualtieri. 
Lamarck, who laid the foundations of the modern generic and 
specific distinction of sea-shells, distinguishes three species of 
Argonauta—Argo, tuberculosa, and nitida (= hians, Solander). 
