8 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



sbowu that the pores are joined together by a canal, and that a nerve 

 probablj' extends along its whole length. In the adult the integument 

 of the first ray of the ventral pair of tins is thrown into numerous nar- 

 row transverse folds. The distribution of the nerves to this structure 

 or its histology 1 have not worked out, but I think it very probable that 

 in it we have a specialized tract of the integument which may be highly 

 sensitive as a tactile organ and be of service to the fish in finding its 

 food on the bottom where it habitually lives. 



I must take occasion here to express my obligations to Mr. Vinal N. 

 Edwards for assistance in obtaining the materials upon which this 

 notice is based. All of the materials were obtained under submerged 

 stones and stumps in the eel pond at Wood's Holl during the latter 

 part of July, 1885. 



EXPLANATION OF THE PLATE. 



Fig. 1. Advanced embryo of Batrachua or Toad-fish, stiU adherent ; the pelvic fin has 

 been translocated forwards. Enlarged about 12 times. 



Fig. 2. An embryo Toad-fish, from the side which has recently ruptured the egg- 

 membrane, a remnant of which still remains around the yelk-bag. The 

 pelvic fin is shown as a small bud-like prominence just behind the pectoral 

 fold. 



Fig. 3. The same seen from above, showing the paired fin folds resting with their 

 bases apparently upon the yelk, outward a little way from the sides of the 

 body of the embryo. 



Fig. 4. Egg of Toad-fish, with spreading blastoderm, in its natural position and ad- 

 herent. 



Fig. 5. A group of four developing eggs of the Toad-fish, adherent to a fragment of 

 bark, to show that the heads of the contained embryos are all directed one 

 way. Natural size. 



3.-OIV THE li:AKIiIJE;K STAGES OF CliEAVAGE OF THE BI.ASTODISK 



OF RAIA ERINACEA. 



By JOHW A. RYDER. 



In the oviparous Bays fertilization of the egg takes place while it is 

 still within the oviduct, or possibly even before it enters the latter. In 

 an egg taken from the cloaca of a female on the 11th of July, 1885, the 

 blastodisk was already segmented into fifteen distinctly-marked cells. 

 The mode in Avhich these were arranged with reference to each other 

 ■showed very plainly that the mode of segmentation, during the early 

 stages at least, is very similar to that which occurs during the develop- 

 ment of osseous fishes, though the cleavage becomes irregular somewhat 

 sooner than in the latter. The sequence in which the segmentations 

 occurred may bo briefly described. 



From a careful study of this disk, which was hardened in chromic 

 acid, the case having first been carefully opened to allow the reagent 

 access to the egg and disk, it is inferred almost with absolute Qertainty 



