364 M. Rathke on the Development of the Decapodes. 



studied structure in its unity,* to follow it out in development, 

 and find the causes of variety to be resolvable into direction and 

 degree ? If the latter method be the easier, Embryology would 

 incalculably facilitate the study of Comparative Anatomy. 



On the Development of the Decnpodes. By H. RATHKE. 

 (Communicated in a letter to Prof. M tiller.) f 



A PRIZE question having last year been proposed by the Na- 

 tural History Society of Harlem, relating to the development of 

 the ten-footed Crustacea, and more especially the crabs, I am in- 

 duced to offer a few remarks on the subject. 



As is already known to you, I formerly endeavoured to prove, in my ac- 

 count of the river-crab, that this animal, when it leaves the egg, is so far per- 

 fected in its form, that it has to undergone farther important metamorphosis 

 until it reaches maturity. Some years afterwards, Thompson advanced the 

 opinion that the Decapodes living jn the sea, as, for examples, the crabs and 

 even the lobster, leave the egg in a very imperfect state, and that they then 

 present a strong resemblance in this respect to the Zoe'a ; thus leading to the 

 inference that, if my observations regarding the river-crab were correct, the 

 latter would present a great anomaly among the Decapodes. In consequence 

 of this, the Harlem Society, much to the satisfaction of all those who have 

 taken an interest in the history of the development of animals, have been in- 

 duced to offer a prize for the best account of the circumstances relating to 

 development which are presented by crabs after their departure from the egg. 

 In this state of matters, I wish to say a few words, which may assist in an 

 examination of Thompson's view, and perhaps also furnish hints as to the points 

 that more especially demand attention in the determination of the question. 



About three years ago, during my residence, for a spring and a summer, on 

 the shores of the Black Sea, I examined the development of about fourteen 

 species of Crustacea belonging to very different orders ; and among others 

 the Eriphia spinifrons, a new species of Palsemon, and a new species of Cran- 

 gon. During the present year, I continued my investigations at Dantzic by 

 examining the Palaemon squilla. I hope to be able in a few weeks to present to 

 the public the work in which an account is given of all my observations. I found, 

 in regard to all the above-mentioned Decapodes, that, at the last period of their 

 uterine life, they possessed just as many tentaculae parts of the dentary ap- 

 paratus and bones, as the old individuals of the same species ; further, that all 

 these organs present the same relative positions, at least in regard to their at- 

 tachment ; and that all these have the same combination and similar forms 

 as in the old individuals. It is only the proportions which, in those parts, 



* It is not intended that human structure should be thus first learned: an 

 acquaintance with it, obtained in the usual manner, is here presupposed. 



t From Mullers Archiv fur Anatomie, Physiologic, und Wissenschafltiche 

 Medicin" 1836. 



