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 thaa 

 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 

 similai", 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 Tr. acutungulus, — 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 Tr. 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 0/ Argonauta. 



Linne comprises all the Argonauta known to him in one 

 species, A. Aryo; his second species, ^. Cywbiuni, is aforamini- 

 ferous shell {Peiieroplis planatus, Montfort), as is proved by his 

 own words, "testa vix minimse arenulse 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). 



