cxlii GENERAL SUMMARY OF SCIENTIFIC AND 



from the earliest stages in the esrsc until all the features of 

 the adult appear. While the mode of segmentation of the 

 yolk is extraordinary, the embryo attains the adult form 

 without any metamorphosis, the changes being very gradual. 

 Mr. Agassiz's observations, with the preceding ones of Miil- 

 ler, Gegenbaur, Kowalevsky, and Pol, give us a tolerably 

 complete view of the mode of development of this order of 

 jelly-fishes. Those Ctenoplwrce on our coast spawn late in 

 the summer and fall. The young brood developed in the 

 autumn comes to the surface again the following spring, near- 

 ly full-grown, to lay their eggs late in the summer. The au- 

 tumn brood most probably passes the whole winter in deep 

 water, and it must take from six to eight months for the 

 young to attain their maturity. The memoir closes with a 

 vigorous and trenchant criticism of Haeckel's "Gastrula" the- 

 ory, exposing its weak points. He regards the assumptions 

 of Haeckel forming the basis of his Gastra?a theory as " whol- 

 ly unsupported." It must " take its place by the side of 

 other physio-philosophical systems;" and he denies that we 

 have been " able to trace a mechanical cause for the genet- 

 ic connection of the various branches of the animal kinsr- 

 dom." 



Professor P. Martin Duncan, in a series of papers on the 

 nervous system of the sea-anemone, substantiates the discov- 

 ery made by Schneider and Rotteken of isolated nerve cells 

 near the pigment cells at the base of the tentacles of the 

 Actinia, supposed to be eyes. In connection with these 

 nerves are certain round refractive cells (Haimean bodies), 

 and other long cells, called the Rotteken bodies. The for- 

 mer, he thinks, carry light more deeply into the tissues than 

 the ordinary epithelial cells. This is also the case with the 

 elongated Rotteken cells, and others similar to them, called 

 bacilli. All these, he believes, with Schneider and Rotteken, 

 when in combination, concentrate light. "When they are 

 brought together in this primitive form of eye they concen- 

 trate and convey light with greater power, so as to enable it 

 to act more generally on the nervous system, probably not 

 to enable the distinction of objects, but to cause the light to 

 stimulate a rudimentary nervous system to act in a reflex 

 manner on the muscular system, which is highly developed. 



A new order of Hydrozoa, called Thecomedusce, has been 



