366 Miscellaneous. 



embryonic band of the Annelids in a still very rudimentary siate. 

 The remainder of the development is reduced to the formation of 

 the oculiform points, a general elongation, the appearance of cilia, 

 &c. 



In the arrangement of the generative organs this species ap- 

 proaches the Turbellaria ; the presence of its circlets of cilia and 

 that of the embryonic band, on the other band, approximate it to 

 the group of Annelids ; and among the latter, Nerilla antennata 

 appears more particularly to approach it in the arrangement of the 

 pharyngeal inflation, and also perhaps of the generative glands. 

 Claparede has already described another type, also allied to the 

 Annelids (Hemidasys aguso), but in its other relations rather ap- 

 proaching the Rotifera. We see, therefore, that the three groups of 

 the Rotifera, Annelids, and Turbellaria become confounded at the 

 base in the common trunk of the Gastrotricha ; and the more parti- 

 cular analogies which the Syllidiaus possess with the latter {Nerilla) 

 show that they must be placed at the base of the Annelids. 



The embryogeny of the group Syllidea has been retarded by the 

 strange nature of the mode of gestation, which has been taken by 

 certain authors for a gemmation upon the parapodes. I have ascer- 

 tained in a great number of species that there was never any thing 

 in it in common with gemmation ; the number of embryos fixed upon 

 each [pair of] parapodes always corresponds exactly with the 

 number of ova developed in each metamere ; in those species which 

 have only one embryo upon each parapode, we see in like manner 

 only two ova in each metamere. I have traced the escape and the 

 complete development of these ova. At a certain period of their 

 development we see the vitelline membrane become confounded with 

 the external integument of the embryo ; the latter then appears to 

 be fixed directly upon the parapode ; and it is this that has led to the 

 belief in gemmation. The most remarkable fact in the development 

 of the ova thus fixed is the complete absence of any larval form ; 

 the relations of the Syllidea to the Gastrotricha allow us to suppose 

 that this absence constitutes the primitive state, and that the state 

 of larva (Trochosphere), afterwards so important, is only derivative. 

 One is accustomed to regard the vermiform state of the embryos of 

 Annelids (Oligocha^ta) as constituting a derivative state ; and it is not 

 uninteresting to remark that side by side with this derivative vermi- 

 form state (Oligochaeta) there exists a primitive vermiform state 

 (Syllidea), by means of which the embryogeny of the Chtetopods is 

 related to that of the Gastrotricha and the inferior worms. In 

 this state the embryonic band (too little known among the ChEeto- 

 pods, in which I have constantly met with it) always exists, and 

 still continues to form the essential fact of the development ; it only 

 begins to be reduced in the Roscoif type. 



To these observations on the lower foims of embryogeny in the 

 Annelids, I may add a few words on the higher forms, some of which 

 have been too widely separated from the ordinary type : Mitraria, 

 among others, may very well be brought back to the general type. 



