ZOOLOGY AND BOTANY, MICROSCOPY , ETC. 13 



other forms. He concludes that, though the nature of the Keimbahn 

 determinants remains uncertain, their origin from metanucleoli, nurse- 

 cells, and possibly the nutritive stream, suggests that they may play a 

 role in the nutrition of the germ-cells during the period extending from 

 their segregation until the formation of the definitive germ-glands. 

 A very full bibliography is appended to the paper. 



Development of Nerves of the Head in Fishes and Amphibian's.* 

 A. Goette has studied this subject in Petromyzon fluviatilis, Torpedo 

 ocellata, Amia calva, and Siredon pisciformis. He first discusses the 

 metamerism of the ecto-mesoderm of the head, and he then passes to 

 particular nerves. The olfactory of Selachians arises from several bud- 

 like outgrowths of the olfactory epithelium and their union into a 

 ganglionic body, which grows centripetally and unites with the brain. 

 In Amphibians, in spite of appearances, it also arises from the olfactory 

 epithelium. 



The auditory of Fishes and Amphibians is not a branch of the facial 

 ganglion; it arises from a proliferation of the labyrinth-epithelium, 

 which forms an associated ganglion. The differentiation of nerve- 

 strands passing from the epithelium into the ganglion gives rise to the 

 formation of the several auditory branches. This is certainly so in 

 Torpedo, and probably so in Siredon. The union with the facial is 

 subsequent and secondary. 



In the vagus complex of the lamprey there are three centrogenous 

 spinal nerves (glossopharyngeal, vagus, and first spinal nerve of the 

 trunk), an ectodermic lateral nerve primordium, and five ectomeso- 

 dermic visceral ganglia. 



In the vagus complex of Torpedo there are united (1) a complete 

 spinal nerve with its own ganglion — the vagus ; (2) four ectomeso- 

 dermic visceral ganglia ; (3) an undivided and non-ganglionated occipital 

 ganglionic ridge, uniting the visceral ganglia and their nerves with the 

 spinal cord ; and (4) a lateral ganglion extending through the whole 

 vagus and occipital region. 



The lateral nerve stem in Siredon does not develop independently of 

 other parts, secondarily sending out lateral twigs to the terminal organs. 

 It arises rather from the commissures which connect the lateral organs 

 and are evoked by them. The lateral twigs are wholly due to the 

 drawing back of the nerve stem from the lateral organs. 



Goette cannot confirm in Fishes or Amphibians the centrogenous 

 origin of the nerves of the eye-muscles or their interpretation as motor 

 roots of the spinal nerves. The fact is that these nerves come into 

 secondary connexion with the brain. They arise as a rule from their 

 muscles or the adjacent mesenchyme, and in rare cases from other nerves. 



These eye-muscle nerves arise from indifferent formative cells which 

 form a syncytium. The fibres arise first in the distal portions and grow 

 centripetally into the brain, where they unite with ganglion-cells. The 

 syncytial primordium forms the sheath as well as the fibres. 



The ganglionic primordia of the lateralis, vagus, and visceral ganglia 

 are at first syncytial. From these syncytia there are differentiated first 



* Arch. Mikr. Anat., 1> Abt., lxxxv. (1914) pp. 1-165 (10 pis. and 6 figs.). 



