IGO bulletin: museum of comparative zoology. 



places a curiously twisted appearance. In some specitneus the chamber 

 above mentioned, at the posterior end of the spinal cord, is occupied by 

 a mulberry-shaped mass of glass-like aspect, from whicli, as from a 

 knotted end, the rod in question emerges, in other specimens the rod is 

 attached to the surrounding connective tissue." Studnicka ('99, p. 9) 

 has also described and figured this "Endknauel'' in tlie ventriculus 

 terminalis of Petromyzon and Myxine. He describes the portion of 

 the fibre forming the knot as of indefinite outline and varicose form, 

 and accounts for its condition in these words : " Der Knoten auf dem 

 caudalen Ende des Reissner'schen Fadens entsteht jedenfalls nicht 

 alloiii in loco, in dem Ventriculus terminalis, snndern der Faden schiebt 

 sich aus dem Canalis centralis (bei den Bewegungen des Thieres?) all- 

 nuihlig in den Ventrikel hinein, und bildet, da er hier wenig IMatz 

 findet den Kniiuel, und wird endlich in der (Jrundsubstanz des lockeren, 

 von Lyniphraumen stark durchgesetztcn Scldeimgewebes aufgelost." 



The explanation of tliis tangled and slirunken condition of Keissner's 

 fibre, as I have seen it in tlio ventriculus ternfinalis, is not difficult. 

 Observations made on the freshly isolated Reissner's fibre of sharks 

 show that it is elastic, and tends to coil and shrink under the action of 

 fixing fluids (pp. 144, 174). It is therefore entirely reasonable to suppose 

 that when, in the fresh condition, the cord was severed, Reissuer'.s fibre 

 recoiled and shrank back into the ventricle, the posterior end l)eing the 

 one at which it was most firmly held. The shrinking and coiling was 

 perhaps augmented by the action of the fixing fluid. A similar coiling 

 of the cut end of the fibre within the fourth ventricle in teleosts is 

 described elsewhere in this paper (p. 211). 



The increased thickness and loss of definite outline may be accounted 

 for in the same way. No such coiling and shrinking has been ob- 

 served in any case where the animal has been fixed before severing the 

 fibre. Studnicka's statement that the end of Reissner's fibre passes 

 out of the sinus of the ventriculus terminalis and into the surrounding 

 lymph space is so at variance with all my observations that I must 

 believe the appearance he so interprets was accidental and due to the 

 disturbed and abnormal condition of the fibre in his preparations. 



D. Sdmmary for Cyclostomes. 



In cyclostomes the optic reflex apparatus is in many respects in a 

 ])rimitive condition, but the relative size of its elements shows it to be 

 of great imi)ortance in the activities of the animal. It is relatively late 

 in development, not being fully established until the second month of 



