32 OBSERVATIONS ON THE DEVELOPMENT OF RAIA BATIS. 



the inward and outward flow of the water which passes through the egg during 

 incubation. 



At the base of each fore horn is a slender projection or spur (c), about half an 

 inch in length, the whole outer border of which breaks up into a series of silky 

 filaments, and these are especially abundant near the free end. Similar filaments 

 are given off from the whole border of the capsule, and all become tangled and 

 woven together in such a manner as to form a broad and somewhat thick mem- 



brane on each side (d). This membrane was found entire only on cases taken from 

 the oviduct, and on those newly laid. In all such, however, as have embryos some- 

 what advanced, it is more or less destroyed, and for the most part only tufts of it 

 remain at the base of each horn. The object of it is not apparent, unless it be to 

 assist in securing an anchorage, by the entanglement of its filaments with subma- 

 rine plants or rough surfaces. 



In a single instance, in the dissection of skates, an imperfect egg-case was found 

 in each oviduct, the development of it having just begun* The hinder horns and 

 the hinder edge of the capsule were the only parts completed. They were contained 

 in the glandular portion of the oviduct, which is quite thick during the : 



ep 



tive season, and is mostly made up of very minute and slender follicles, of great 

 length. From some of them fibrils protruded, identical in structure with those out of 

 which the cases are made, and which, after being liberated, are doubtless moulded into 

 the shape of these cases, and cemented together by some secretion from the oviduct. 

 The horns are formed in grooves on either side of the duct, and the pouch for the 

 yelk in the intervening space, t A careful examination of the ovary and oviduct in 

 the above instance showed the singular fact, that, although some of the yelks were 

 mature, none had as yet been detached from the ovisacs. This circumstance ren- 

 ders it probable, that, after the horny pouch is partially formed, the yelk descends 

 and enters it, and that then the other portions are completed. If this supposition, 

 based upon a single observed instance, were 



to be confirmed by further 



it would prove the existence of an interesting deviation from a rule among animals 

 generally supposed to be without exception, viz. that the presence of the yelk in the 

 oviduct is necessary before the formation of the egg-coverings can be-in. 



indebted to my friend Dr. John Green of Boston. 



am 



t Ari 



£ga of Plagiostomes. See Hist, of Animals, Book VI. Section 10. 



Thesaurus 



bryo in situ. Cuvier ascribes the materials of the case to the follicles, and the form to the glandular surface. 



Lego 



