94 PEOF. ALLMAN ON THE 



mentation of tlie vitellus presents tlie features characteristic of 

 all tlie Ctenophora hitherto examined. He has traced its deve- 

 lopment up to the formation of the series of swimming-plates, 

 which he describes as composed, like those in EschscJioUzia, of 

 confluent hairs. At this period the young Cestum has a globular 

 form ; and the tentacles are of considerable length, and are quite 

 similar to those of Uucharis. 



The development of JEucJiaris multicornis, of Cydippe hormo- 

 phora, and of Pleurolrachia has also been studied by him ; and, 

 so far as his observations have gone, he finds the development of 

 these Ctenophora to take place quite on the type of that of 

 Jilschsclioltzia. 



Kowalewsky has further examined the development of Beroe 

 MrsTcalii ; and, though he has but a slight acquaintance with my 

 own published researches on the development of Beroe ovata, he 

 confirms, in their essential features, most of the results to which 

 I had already arrived. 



Some observations on the development of the Ctenophora have 

 also been made by Fol, and published by him in the form of an 

 inaugural dissertation *. 



He describes the structure of the egg in JEurampJicea vexillifera, 

 Gegenb., his account of which agrees m all essential points with 

 the previously published descriptions of the egg of other Cteno- 

 phores. He has observed also the phenomena of segmentation, 

 and has seen the formation of both the large and the small 

 segment-spheres, and the envelopment of the former by the 

 latter. He appears to have seen the difierentiation of the four en- 

 dodermal masses which are to become the primordial trunks of the 

 vascular system ; but he does not seem to recognize their signifi- 

 cance ; while his account of the formation of the digestive cavity 

 and funnel is but fragmentary, and, judging from the analogy of 

 other species, is less in accordance with the actual course of the 

 development than are the descriptions which had been previously 

 published. His account of the proper embryonal development 

 does not go beyond this stage ; and the few further details which 

 he gives us, apply to bhe young Ctenophore in a much more ad- 

 vanced stage of growth. 



* Hermann Fol, ' Ein Beitrag zur Anatomie und Entwickelungsgeschichte 

 einiger Eippenquallen/ Berlin, 1869. 



