480 Miscellaneous. 



I reserve for a more detailed memoir the investigation of the for- 

 mation, segmentation, <fec. of the single ovum, and I shall confine 

 myself at present to calling attention to some points of the organization 

 of the hatched tadpole-like larva. The large vesicle which I regarded 

 as the first rudiment of the common cloaca has certainly this physio- 

 logical signification ; hut its morphological importance is greater than 

 I had supposed. 



This part, in fact, possesses the value of an individual ; that is to 

 say, it is the homologue of the Cyathozoid of the embrj^o of Pyro- 

 soma. The arrangment of the other Ascidians relatively to this 

 vesicle is exactly the same as that of the young Ascidiozoids of 

 Pyrosoma relatively to the Cyathozoid. To^be convinced of this 

 it is only necessary to compare Kowalevsky's fig. 54, pi. xli. with 

 the figure given by me for Astellimn, in my ' Recherches sur les 

 Synascidies ' (pi. xxvi. fig. 6). To render this comparison perfect 

 we must revex'se the figure of the Pyrosoma, and turn it 45° from 

 right to left round a longitudinal axis. The presence of a very 

 abundant white pigment renders the continuous observation of the 

 embiyos of the Diplosomidse very difficult, and prevented my per- 

 ceiving this remarkable agreement. 



The differences of structure which exist in the adult state between 

 the branchiae of Astellium and Pyrosoma are in relation to the 

 different modes of existence of these animals. Moreover the em- 

 bryos of an allied group, the Botryllidae, have a branchia which 

 astonishingly resembles that of Pyrosoma. 



"We may therefore regard the Diplosomidse as representing the 

 fixed state of a type of which Pyrosoma is the swimming or pelagic 

 form. Consequently the group Lucise of Savigny may be divided 

 into two families, Pyrosomidse and Diplosomidae, presenting recipro- 

 cally the same relations as the Siphonophora and the Hydriformes 

 among the Acalephan Coelenterata. 



A last fact which is important to indicate is, that in the pecu- 

 liarities of the development of the Luciae (defined as we have just 

 seen) we find a new application of the law enunciated by us as 

 the consequence of our embryogenic investigations on the group 

 Molgulidae. The Pyrosomidse, which live free, present an abridged 

 and condensed development, a partial segmentation, and an anurous 

 erabiyo destitute of organs of sense ; while the sedentarj'^ Diploso- 

 midae in the adult state have a dilated metamorphosis and a 

 urodelous embryo, furnished with a well-developed visual and audi- 

 tory apparatus. I may add that the tadpole-like larva of Astellium 

 sponyiforme possesses a caudal appendage, the musculature of which 

 is very complex, while its membranous pait is traversed by horny 

 filaments, like those described by us in the simple Ascidians of the 

 group Cynthia and in the Synascidians of the genera Botryllns and 

 Botrylloides. 



Lastly, in Astellium, as in Ascidia scahra, Miiller, and A. gelatinosa, 

 Kisso, the tunic of cellulose is formed independently of the embryo, 

 during (and even before) the segmentation of the vitellus. However, 

 this process is less distinct than in the Ascidians in which we have 

 observed it. — Comptes Jintdiis, December 13, D^75, pp. 1214-1216. 



