NOTE OX THE EYES OF CARDIUM MUTICUM Ikeve. 2SS 



ill dirtereiit stages of dei'dojninni. we ••an study their formation 

 from their sections. It seems to me that the eyes of CardiiDii develoj) 

 ill two wavs. Althoiiuii we must regard botli as more or less al)ljrevial- 

 ed, vet we can ilistiuguish one as //(/' iiioir ahhnciaicd proo'ss from the 

 (jther ///<• l('ss aJihrcnated. If an investigali«j]i into their development 

 could be made in immature spe<-imens. mcjre satisfactory resiiUs would 

 doubtless be obtained, unless they are as in the young oï Veclcii in wliicli 

 Patten was disa])j)oint€d to lind any abbreviated development of tlie 

 eye. I shall describe the less ahhrerlaled process of development tirst. 



Tiiere first forms on the tip of a tentacle (tig. .'>) an invagination 

 the mouth of wliich then closes (tig. 4). Thus a solid mass of cells is 

 produced, with a slight conca\ity at the place where the mouth of the 

 invaoination at tirst opened, and this is turned towards the siphonal 

 opening. it consists of cells in many irregular rows, while tiie general 

 epithelium consists of columnar cells in one row. A ner\e running 

 aloDii' the central axis of the tentacle touclies the lower surface of the 



Ci 



(•ell mass and there divides anteroposteriorly into two branches. 



In the upjter jtart of the cell mass, a s])herical j)ortion becomes 

 differentiated and sei)aratcd from the rest by a basement membrane 

 (tig. 5). This spherical portion is the rudiment of the lens, which is 

 therefore epiblastic in origin, not mesoblastic as in the case of the eye 

 of Pecten, according to Patten. The cells constituting the rudimentary 

 lens are large and some of them have nucleoli. At this stage, 

 although the lens is differentiated and separate from the surrounding 

 cell mass, it is still imbedded in ihe epiblastic thickening. 



In the next stage (fig. 6) the epiblastic thickening surrounding the 

 lens is obser\ed to be separated into two parts — an up|X3r and a lower. 

 The upper i)art is continuous with the general e])ithe!ium and consists 

 of fiat cells in (jne row. It is the cornea. The lower part is cup- 

 shaped and is n«3t connected with the general e})ithelium. It consists 



