744 Central Notes. [September, 



alternate exhaustion and restoration of excitability, and thus ner- 

 vous energy is economized. Thus, in creatures not possessed of 

 ganglia, rhythmic action results alone from this alternate exhaus- 

 tion and restoration of muscular excitability, causing the constant 

 stimulation to alternately fall below and rise above the limits of 

 adequacy. 



Ova of Echidna hystrix. — Professor Owen has examined the 

 ova of two specimens of IxhiJna hystrix as they occurred in situ. 

 The ova increase in size prior to embryonal development, attain- 

 ing a diameter of six millims., but evidence of the viviparity of 

 the animal is found in the commencement of the fissure of the 

 germ-mass. Previous observations have proved that the teatless 

 mammary glands acquire large development during gestation, and 

 that the lacteal aureola becomes lodged in a te^umentaiy depres- 

 sion or quasi pouch, capable of receiving the head and fore limbs 

 of the young when this is not more than one inch ten lines in length. 



Zoological Notes. — Professor Haeckel has returned from his 

 expedition to Ceylon, and has sent over fifty cases of specimens 

 to Jena. His researches on the Ceylon coral reefs were highly 



successful. M. Thury has published a hypothesis on the origin 



of species in the Archives des Sciences Physiques et Naturelles, 



Feb. 15. In a recent communication to the French Academy, 



M. Huet records the discovery of segmental organs in certain 

 isopod Crustacea. It appears, says Nature, that Mr. Arthur 



eggs originally obtained from the Thames, England, found that 

 the annual increase of weight had risen from I vj to 2 ' _< pounds, 

 and an example had been seen weighing twenty pounds. The 



found increased from thirty-three to fifty, as exemplified in British 

 fish, to from forty-three to fifty-four in the New Zealand examples, 

 showing that these organs are inconstant as to numbers. These 

 fish, moreover, living in different streams in New Zealand, had also- 

 assumed local peculiarities of size and changeof form. The U.S. 



Fish Commission is issuing the first volume of its Bulletin; the 



; ; ' . ■ . , ■" , _,^ .. \ ;■.'..'..■,;-.' : * 



four-spined stickleback, the Spanish mackerel, the shad and the sea- 

 horse {inppocauiMts antiquarian). lie states that the bony fishes 



mentation-ca n d r the head to form the 



heart. The true gastrula of Teleosts appears to originate as an 

 invagination at the tail of the embryo, represented by Kupfler> 

 canal, essentially the same as in Amphioxus, and is not homolo- 

 gous with the gastrula regarded as such bv Haeckel. The paired 

 fins originate fn ,m lateral to!, is, and the fir-t skeletal elements of the 

 breast fins in the cod are a pair of curved cartilaginous arcs or rods. 



