68 MEMOIRS OF THE NEW YORK ACADEMY OF SCIENCES 



is lost. In the toad-fish (Batrachus) according to Miss CLAPP ('91) the caudal end 

 of the embryo parts company with the margin of the blastoderm at a relatively 

 early period (figure 30, A, B, C). EYCLESHYMER reports a similar condition for 

 Lophius, though his description and figures do not bear out such a contention. The 

 latter author infers from certain appearances that the same process occurs in Amiurus 

 as well. In this, EYCLESHYMER is certainly wrong. The embryo of this fish in- 

 variably retains its connection with the germ-ring until the complete closure of the 

 yolk blastopore. JHERING, also, ('88) has described what seems to be a similar 

 condition for the South American cat-fish Arius. The eggs of Batrachus, Lophius and 

 Anus are all extraordinarily large, the latter being as much as 18 mm. in diameter. 

 Again, CORNING ('96) reports this separation of the caudal end of the embryo from 

 the germ-ring to exceptionally occur at a relatively late period in the salmon. 



It will be recalled that Amia was included among the forms exhibiting the "pro- 

 stoma," although it is now certain that the egg of Amia is a holoblastic one. How- 

 ever this may be, the egg of this ganoid is probably secondarily holoblastic, for it 

 shows other evidences than the one considered of having been derived from a mero- 

 blastic egg. For instance, my discovery in Amia (SUMNER, '00, a) of a rudimentary 

 syncytium or "periblast" with typical giant nuclei confirms the above view (figures 

 16 and 17) although this fact is also open to the interpretation, as Professor Mi not 

 has suggested to me, of being anticipative of the condition found in the teleost rather 

 than derived from that in the shark. I do not, however, offer the case of Amia as 

 being nearly as well established as that of the teleosts mentioned. 



V. CONCRESCENCE AND CONFLUENCE. 



Problem Stated. In the foregoing pages concrescence has been discussed only 

 in relation to that process by which the hinder end of the embryo becomes folded 

 off from the margin of the blastoderm. It will be remembered that BALFOUR ('81), 

 while admitting the occurrence of concrescence to this extent, denied to it any part 

 in the formation of the embryonic body itself. So far, I have affirmed the process 

 only to the degree admitted by BALFOUR. 



I cannot go further, however, without facing the general problem of concrescence. 

 I must defer to a subsequent paper a review of the endless mass of literature bearing 

 upon this interesting subject. In this article, I shall merely point out that my conclu- 

 sions are quite in harmony with the results reached by the two investigators who have 

 given most labor to the experimental study of concrescence in the teleost embryo. 



