330 Canadian Record of Science. 



on the main sympathetic stem, &c., seen in the Terrapin ; 

 and the figure given in Plate (fig. 4) is intended to show- 

 in a general way the condition of things present in the 

 Terrapin and C. my das. 



But as no satisfactory description for physiological pur- 

 poses has been published for the marine turtles, I shall 

 describe what' I have found on the examination of a large 

 number of cases. So much difference has been found in 

 individuals, and the general plan is so disguised, that it was 

 only after considerable examination and comparison that 

 the typical structure could be defined. 



In C. caretta and C. imbricata, the great size of the sympa- 

 thetic in the neck, almost equal to that of the vagus, is in 

 striking contrast with the condition in 0. mydas, which has 

 the sympathetic scarcely larger than in the Terrapin ; also 

 in the two first-mentioned species the vagus and sympa- 

 thetic run widely apart throughout their whole course ; in 

 0. mydas, as in the Terrapin, they sometimes fuse, but not 

 inseparably. 



As regards the condition existing at or near the entrance 

 of these nerves into the skull, much difference in details has 

 been found. 



In the Loggerhead and Hawksbill there is always more 

 or less fusion above at this point ; but in some cases there 

 does not seem to be any genuine blending, for the nerves 

 (vagus, glosso-pharyngeal, and sympathetic) are separable 

 by a " seeker." There is a slight cord-like swelling in the 

 sympathetic, and beyond this, two separate divisions enter 

 the skull together, and do not seem to have any close con- 

 nection with the sympathetic. 



In these two species I have never found above any such 

 well-defined fusion as exists in the Terrapin and C. mydas. 



But by far the most remarkable condition found in C. 

 caretta and C. imbricata is that seen in the third ganglion of 

 the sympathetic stem. It was only after finding a case like 

 that shown in fig. 3 that it became clear that in this ganglion 

 the third and fourth ganglia of the stem were fused together ; 

 but when C. mydas was examined, it was seen that fusion was 

 not, in that species, the rule, but the exception, as in the 

 Terrapin. 



