50 The Microscope. 



problem, and claims that it is the rudiment of the primitive 

 gastrula cavity, a conclusion not in the slightest warranted by 

 facts. He also discusses some points of vertebrate morphology, 

 but failing to understand the process of gastrulation in the 

 teleosts, he succeeds no better here. His account of the origin 

 of the eye of the vertebrates, is really that of Lankester, and 

 adds nothing to it. It does not even attempt to explain the 

 difficulties pointed out by Balfour. 



Mr. George Brook, jr., in the same number with the paper 

 by Mr. Cunningham, attacks another fish problem, that of the 

 origin of the hypoblast. He would deny the existence of any 

 invagination of the primary cell layers to form the hypoblast, 

 but derives that layer wholly from the parablast or interme- 

 diary layer. 



In a second paper in the same journal, to be noticed bye- 

 and-bye, Mr. Cunningham returns to the fishes, and one sen- 

 tence may be quoted. Referring to the formation of the polar 

 globules, and the spindle formed in connection with them, he 

 says (p. 132): "As is well known a direction spindle has been 

 sought in vain in the ova of vertebrates, and the expelled ele- 

 ments in these are not globular in form. Hoffman alone has 

 described an amphibaster de rebut [polar globule spindle] 

 in Teleostean ova, but has not traced its history." In his first 

 paper Mr. Cunningham showed himself acquainted with the 

 papers of Kingsley and Conn and Whitman and Agassiz on the 

 development of the teleosts. Had he read them or the various 

 papers of Ryder, carefully, he would have seen that his state- 

 ment is all wrong. There is a direction spindle, its history has 

 been traced, and the polar globules in the teleosts are spherical. 



A Nervous System in Sponges. — Dr. von Lendenfeld has 

 discovered in some of the calcareous sponges cells which he 

 regards as sensory in function. In his preliminary account (Z. 

 A. viii., p. 47, 1885) he describes them as forming a ring in the 

 walls of the pores of the Sycones, and distributed in bunches 

 irregularly over the surface of the Leucones. These sensory 

 cells are long and fusiform, and are arranged at right-angles to 

 the surface ; they are also said to be mesodermal and do not 

 appear as modifications of the ectoderm, a conclusion which is 

 at variance with the sensory element in other groups. His 



