The finer Structure of the Nerve Cells of Invertebrates. 5J 



On the Presence of Centrosomes and Spheres in the Oanglion 

 Cells of Selix ijomatia. 



The writers, who have thus far contributed to our knowledge of 

 these structures in nerve cells, are for the nerve cells of Vertebrates, 

 V. Lenhossék (18), BuEHLER (3), Dehler (5) and Schaffer (39); 

 for the nerve cells of Invertebrates, Miss Lewis (19) and myself (22). 

 In addition to the above, Rohde (38) has recently published a 

 remarkable paper upon the mode of increase and growth of the 

 ganglion cells of Gastropods, but makes no reference to the presence 

 of centrosomes and spheres. 



So far as known to the writer, v. Lenhossék's paper (18), which 

 appeared in November 1895, described for the first time the existence 

 of centrosomes and spheres in certain of the moderate-sized spinal 

 ganglion cells of the frog. This interesting discovery led the writer 

 to search for similar structures in the ganglion cells of Invertebrates, 

 in which they had likewise never been found. The result of this in- 

 vestigation was that, of all the ganglion cells examined {Astacus, 

 Camharus, Homarus, Lumhricus, Limulus, Helix, Arion and Limax), 

 only those of Helix, with the possible exception of Limulus, showed 

 the presence of structures which might seriously be taken for centro- 

 somes and spheres. 



The appearance presented by these structures in the ganghon 

 cells of Limulus were so vague as compared to those in Helix, that, 

 at the present writing, I feel compelled to disregard their existence. 

 A brief outline of these results was embodied in a paper which 

 appeared in May 1896. Soon after the appearance of this paper, one 

 appeared, written by Miss Lewis, entitled "Centrosome and sphere in 

 certain of the nerve cells of an Invertebrate", In this paper she de- 

 scribes the existence of these structures in certain of the nerve cells 

 of a new species of worm belonging to the Annelid family Maldaniae. 

 In view of the results obtained by Morgan (23) on the pro- 

 duction of artificial astrospheres in ova, and of the similar results 

 obtained by my Assistant, Ulric Dahlgren (4), in the spinal ganglion 

 cells of a dog, one cannot be too conservative in estimating the value 

 of these structures thus far found in nerve cells. I feel quite sure, 

 however, that the majority of the structures thus far described in 

 nerve cells as centrosomes and spheres are genuine. But, since I 

 have seen Dahlgren's preparations, I am thoroughly convinced that 

 the possibilities of producing artefacts of this character are so great, 



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