157 



Prof. Jeffries Wyman made some remarks on the Foetal 

 Zygcenttj (Hammer-headed Shark,) presented at the pre- 

 ceding meeting by the Secretary. 



The specimen is six and a half inches long. It has the gen- 

 eral fornn and appearance of the adult, except that the outline of 

 the head is less regular. All the fins are well formed ; between 

 the pectoral fins is the remnant of the pedicle of the vitelline 

 sac. This specimen (the history of which is not known) was 

 probably taken from the oviduct, as the external branchial fringes 

 which exist, in the early periods, in all plagiostomes, are still 

 persistent. An opening was made into the abdomen, but the parts 

 were not in condition for minute dissection ; no trace of an in- 

 ternal portion of the vitellus was found. No teeth are devel- 

 oped, but there exists, both in the upper and lower jaw, a deep 

 dental groove. 



Prof. Wyman also gave an account of some observations 

 vi'hich he had recently made on Hybernating Insects. 



He had examined chrysalids of the common Mud Wasp, a 

 species of Pelopceiis, and found that they were not frozen during 

 the coldest weather. On the morning of February 7th, when 

 the thermometer had been - 18° F. and had risen to about 

 -8° F., they were still unfrozen, and when removed from their 

 pupa cases, made obvious muscular motions. The pupa preserved 

 its usual transparency and flexibility ; when crushed upon the 

 surface upon which they rested, the fluids of the body instantly 

 became opaque and were congealed. The question naturally 

 presents itself, as to the source of the heat which enables them 

 to preserve their temperature, when exposed to so low a degree 

 of cold. The non-conductors by which they are surrounded, 

 consist of a casing of mud, and within this a tightly woven, but 

 thin, silky cocoon. It would seem that so small a body, exposed 

 to cold so intense, must have an internal source of heat. Prof. 

 Wyman had also examined the eggs of the Moth of the Canker- 

 worm, and found their contents unfrozen. 



Dr. A. A. Hayes read an extract from a letter of Dr. C. 

 F. Winslow, of San Francisco, on Earthquakes. 



