164 Papers from the Marine Biological Laboratory at Tortiigas. 



Figs. 1 and 2. — Longitudinal sections of tlie advanced plannlse, showing the columnar 

 ectoderm, the more or less solid endoderm, containing irregular or radiating cavities, 

 and the ectodermal invaginations which lie between the ectoderm and endoderm and 

 are of doubtful significance. An ectodermal invagination at the narrower pole of 

 fig. 2 mav represent the stomoda?aI invagination. 



As compared with the development of other medus;e, the entire embry- 

 ology of Linerges is characterized by the regularity of the processes of 

 cleavage and gastrulation ; and although this regularity may suffer certain 

 modifications, without preventing the formation of a normal planula, there 

 is in this species none of that extreme irregularity which characterizes the 

 development of Pciniaria (Hargitt. 1904). 



EXPERIMENTS. 



Isolation of blostoincrcs. — My observations on the development of parts 

 01 the unsegmented egg and of isolated blastomeres are essentially similar 

 to those of Zoja (1895) and Maas (1905). Parts of the unsegmented but 

 fertilized egg may give rise to swimming larvae; these are almost certainly 

 the parts containing the egg and sperm nuclei. Isolated blastomeres, at 

 least as late as the 4-cell stage, give rise to swimming larvae, which are ap- 

 parently normal; however the lack of clearly differentiated organs in the 

 planula makes it difficult to determine in this stage whether the larvae are 

 wholly normal or not. When the egg fragments are small, or when the 

 blastomeres are isolated at a late stage of the cleavage, the blastoccel is rela- 

 tively small and the gastrulation is not normal. These results are essentially 

 like those obtained bv all investigators of the development of the Cnidaria. 



