422 



shows that butterflies effect the cross-fertilization of Alpine orchids. 

 It seems that from twelve to fifteen per cent, of the orchids of the 

 lowlands are fertilized by Lepidoptera, while from sixty to eighty 

 per cent, of Alpine orchids are fertilized by the same kind of in- 

 sects. This corroborates, he says, his view that the predominant 

 frequency of butterflies in the Alpine region must have influenced 

 the adaptation of Alpine flowers. 



Muller has also shown the wonderful modifications brought 

 about in the legs and mouth-parts of bees by their efforts in fertil- 

 izing flowers. 



ZOOLOGY. 



On the Development of the Nervous System in Limulus. 1 — 

 After a good many unsuccessful attempts at discovering the first 

 indications of the nervous system in the embryo of Limulus, I at 

 length, in making fine sections, with the aid of the skill of Prof. T. 

 D. Biscoe, discovered it in a transverse section of an embryo in an 

 early stage of development, corresponding to that figured on plate 

 iv, fig. 10, of my essay on the Development of Limulus Polyphe- 

 mus in the Memoirs of the Boston Society of Natural History. 

 The period at which it was first observable was posterior to the first 

 blastodermic moult, and before the appearance of the rudiments 

 of the limbs. The primitive band now surrounds the yolk, being 

 much thicker on one side of the egg than on the other, the limbs 

 budding out from this disk-like thickened portion which represents 



was observed it was entirely differentiated from the nervous layer 

 proper, and in section and relation to the nervous layer appeared 

 much as in Kowalevsky's figure (33) of the germ of Hydrophilus 

 (Embryologische Studien an Wurmen und Arthropoden, 1871). 



At a later stage in the embryo, represented by PI. V, fig. 1 6 in 

 my Memoir, at a period when the body is divided into a head and 

 abdomen, and the limbs are longer than before, by a series of sec- 

 tk>n> parallel with the under surface of the body, I couM mak>' 

 out quite satisfactorily the general form of the main nervous cord. 

 It then forms a broad thick mass, the two cords being united, with 



segments and situated between the primitive ganglionic centres. 



