DEVELOPMENT OF THE CTENOPHOEA. 97 



The interesting observations of Kowalewsky regardiuo- tlie 

 formation of the gelatinous tissue have been confirmed by Agassiz 

 who has seen this tissue pervaded by celLs, which have detached 

 themselves fi-oni the outer walls, and migrated into the gelatinous 

 mass. 



The vessels are described as originating in four outbulgino-s of 

 the digestive cavity, which rapidly push their way towards the 

 oral pole. These tubes, as pointed out in the abstract cited above 

 (see p. 91), really result from the transformation of the four 

 great endodermal sacs, whose cavities are continued from the 

 central cavity of the embryo, which ought to be distinguished 

 from the true digestive cavity, being the part which is to become 

 the so-called funnel of the adult. 



Agassiz had already described * some of the more important 

 stages in the post-embryonal development of PleurohracJda 

 (CydipidiB) and of Mertensia, as well as in that of Bolina, which 

 may be taken as a typical example of the lobate group of the 

 Ctenophora, and had illustrated his memoir with many beautiful 

 and highly expressive woodcuts. In the present memoir he has 

 made a ver}"" careful study of the entire embryology of Fleuro- 

 hracliia, and has shown that, setting aside the formation of the 

 long retractile tentacles, which are absent in Beroe, it is in all 

 points almost identical with that of Beroe. He has also shown 

 that the changes undergone by the young Mertensia during its 

 post -embryonal development, have an almost complete identity in 

 all essential points with the post-embryonal changes of Pleuro- 

 hracliia. 



"While the changes of Beroe, Bleurohracliia, and Mertensia 

 during their post-embryonal development are not by any means 

 striking, those presented by Bolina are on the contrary shown 

 to be very great — a fact to which, in some important points, 

 MacCrady had already, as cited by Agassiz, called attention. Up 

 to the time when the young Bolina is ready to escape from the 

 egg it can scarcely be distinguished from Pleurohrachia during a 

 corresponding period, except in the fact that the compression of 

 its body is in a plane at right angles to that of the compression 

 in BleurohracMa. It is after this that we find those well-marked 

 changes of form, which show themselves in the acquisition of 



* Alex. Agassiz, in lUustr. Catal. of Museum of Couap. Zool. Harvard Col- 

 lege, 1865. 



