THE ADHESIVE ORGANS OF AMIA. 



ALBERT C. EYCLESHYMER and JAMES MEREDITH WILSON. 

 From the Anatomical Laboratory of St. Louis University. 



Most of the ganoid fishes have adhesive organs or sucking 

 disks in the early stages of their development. 



These organs have received little attention even from morpho- 

 logists and systematists. Their development has not been 

 worked out with any completeness in any species, but enough 

 has been learned to raise numerous questions. The earliest stages 

 in their development have never been described ; even the germ 

 layer from which they take their origin is unsettled. Their rela- 

 tions to other systems, digestive system, nervous system, etc., are 

 in dispute. The various stages in their development, their 

 structure during these stages and the functions they perform, as 

 well as questions of their ultimate fate and their phylogeny and 

 meaning seem to us to merit further study. 



In a previous paper ('06) on the " Development of Amia " 

 we have touched briefly on these organs. The present paper is 

 a continuation of the same subject and is based on the same 

 material. 



Description of Stages. 

 The anlagen of the adhesive organs appear in the embryo about 

 seventy hours after fertilization, or more precisely, when the em- 

 bryo extends over about 160 degrees of the circumference of 

 the egg. A median sagittal section of the anterior portion of an 

 embryo of this stage is shown in Fig. I, The ectoderm consists 

 of a single layer of cells externally (s.ec.) and a large mass of 

 deeper lying cells; the deeper layer is some 15 to 20 cells in 

 thickness. In this mass of cells which forms the anlage of the 

 future brain there is a slight cavity (br.c.) which is the first cav- 

 ity to appear in the brain. In front of the brain is a second 

 mass of thickened ectoderm (p.cb.) which has been called the pre- 

 cerebral mass. The gut-cavity {g.c.) is now widely extended 

 laterally. In its anterior portion its dorsal and ventral walls are 



i34 



