OF Tilt; INVEIITEEKATE ANIMALS. 35 



We here find, in regard to the minute structure, a remarkable 

 agreement between the form and elementary constitution of the 

 material substratum, and an infinitely more remarkable fact for 

 general comparative physiology, and especially for these animal 

 forms. For these organisms, the whole life of which can scarcely 

 be considered as more than a mere vegetation, a constant process 

 of assimilation, and the whole nei-vous system of which is re- 

 duced to its simplest elements, a single ganglion (sympathetic?) 

 with a pair of primitive fibrous bundles running from it, are 

 placed in a vegetable envelope. According to the observations 

 of Milne-Edwards*, the Ascidia in their young state swim about 

 unattached, and do not become fixed until a certain period of 

 their existence. We might imagine that in this case a luxurious 

 condition of simple cellular tissue, which we might call an Alga, 

 or something of that kind, surrounded the animal in the form of 

 a pouch, and thus formed with it a zoophyte in the true sense of 

 the word, did we not find in this sac, on the one hand, the per- 

 fect branched vascular system, — thus organic connexion with the 

 purely animal organic systems of the animal ; — and did not, on 

 the other hand, the observations of Sarsf and Milne-Edwards J, 

 on the development of the compound Ascidia {Botryllus, Polycli- 

 num, &c.), oppose this view ; for in them the earliest formation 

 of this sac appears during the process of bifurcation in the form 

 of a transparent, colourless, gelatinous layer, between the enve- 

 lope of the ovum [chorion ?) and the yolk. 



Chemistry has here done all that it can ; further explanation 

 must be obtained from morphology. A new fundamental study 

 of the development of this animal, with especial regard to the 

 histogeny of its envelopes, must solve the enigma, and under the 

 present circumstances would prove of the greatest interest. 



We shall conclude this investigation with a consideration of — 



5. The Zoophytes, 

 in one of their simplest representatives, which has been before 

 mentioned, Frustulia salina, Ehrbg§. Its discoverer first found 

 it in quantity in the Konigsborner saline spring. As is well 

 known, W6hler|| two years ago made the observation which is of 



* Observations sur les /Iscidies composees des cotes de la Manche. Paris, 1841. 

 Condensed by Von Siebold in the Annual Report of Mailer's Archives, 1842, 

 p. clxxx. t Froriep's Nolizen, iii. 1837, p. 100. 



X Loc. cit. § Loc. cit. p. 232. 



II Wohler and Liebig's vlnnalen, 1843, p. 20G. 



D 2 



