30O ECTOPROCTA. 



right in regarding this as the stomodaeum, it is probable that it 

 never unites with the invaginated hypoblast, and that the 

 alimentary tract of the larva remains therefore permanently in 

 an imperfect condition. 



Careful observations have been made by Repiachoff (No. 318) on the 

 early development of Tendra, which accord in some respects with the 

 results arrived at by Barrois in his second memoir. The observations are 

 not, unfortunately, carried down to the complete development of the larva. 



The ovum divides in the normal way into two and then four uniform 

 segments. These four next become divided by an equatorial furrow into 

 four dorsal and four ventral segments, the former constituting the aboral 

 pole and forming the epiblast, and the latter the oral pole. The stages with 

 sixteen and thirty-two cells appear to be formed in the same manner as in 

 Alcyonidium but between the two layers of cells forming the oral and 

 aboral poles a well-marked segmentation cavity arises at the stage with 

 sixteen segments. At the stage with thirty-two cells the four middle cells of 

 the oral side, which are larger than the others, become divided into two 

 tiers, in such a manner as to form a prominence projecting into the 

 segmentation cavity. By the appearance of a lumen in this prominence 

 it becomes converted into an archenteron, which communicates with the 

 exterior by a blastopore in the middle of the oral surface. The blastopore 

 becomes eventually closed. 



The archentenc sack of Repiachoff is clearly the same structure as 

 Barrois' four invaginated cells of the oral face, their further history has 

 unfortunately not been followed out by Repiachoff. 



The free larva swims about for some time, and then fixes 

 itself and undergoes a metamorphosis ; but the exact course of 

 this metamorphosis is still very imperfectly known. 



According to the latest statements of Barrois the attachment 

 takes place by the oral face 1 . The ciliated disc, which in the 

 free larva forms a kind of cup directed towards the aboral end, 

 turns in upon itself towards the oral face. It subsequently 

 undergoes degeneration and forms a nutritive or yolk-mass. 

 The skin of the larva after these changes gives rise to the 

 ectocyst or cell of the future polype. The future polype itself 

 appears to originate, in part at any rate, from the so-called 

 dorsal organ*. 



1 Barrois himself held the opposite view in his earlier memoir, and other observers 

 have done the same. 



* The statements on this head are so unsatisfactory and contradictory that it does 

 not appear to me worth while quoting them here ; even the latest accounts of Barrois, 

 which entirely contradict his early statements, can hardly be regarded as satisfactory. 



