1902.] NATURAL SCIENCES OF PHILADELPHIA, 293 



contour line. Another striking feature of the epithelium Is the 

 rectangular arrangement of the cells in longitudinal and transvei-se 

 rows. One exception occurs at the posterior end of the typhlosole, 

 at which point the longitudinal rows converge, so as to form, as 

 Schonichen says, " parallel parabolas, making a picture in optical 

 section not unlike a longitudinal section through a vegetative 

 point." While the rows elsewhere are rectilinear, they are not 

 often continuous from one end of the " mid-gut" to the other. 

 I have often seen longitudinal rows which terminate some distance 

 from the end. Discontinuous transverse rows have also been seen. 

 Ide's fig. 19 shows these features, which are supported further by 

 his statement that only the median two ventral rows can be followed 

 uninterrupledly from the anterior to the posterior end. 



(1) Growth of Intestine. 



At first sight the number of rows of cells appears definite and 

 constant enough that one might name the cells as city blocks are 

 named, and might even find cell homology between different indi- 

 viduals. This character has been mentioned by all the authoi-s since 

 Lereboullet (8) (Huet, Ide, Conklin, IMcMurrich, Schonichen), 

 and ^NlciMurrich has attempted to show that the number is constant 

 throughout the life of an individual. McMurrich's attempt is 

 based on the non-occurrence of cell division. No observer except 

 Lee (9), who regarded certain deformed nuclei stretching from one 

 cell to another as remains of the spindle {fiiseau de regression), has 

 seen any sign of mitosis, and McMurrich says : " I have never been 

 able to satisfy myself that normal amitosis actually occurs." He 

 seemed to be justified, therefore, in the attempt (which by his 

 own confession is not wholly successful) to show that growth of 

 the intestine takes place by enlargement of the cells rather than by 

 multiplication. 



Amitosis. — In young individuals amitosis is by no means rare. 

 Fig. 2, A, B and C, show some of the stages which are easily 

 found at this time. Fig. 2, A, is a longitudinal section exhibiting 

 the relative sizes of cells whose nuclei have just divided, and of 

 those recently constricted off. Conklin (I. c.) has rightly interpreted 

 this constriction of the cells, and has figured what he regards as an 

 amitotic division. It would appear from fig. A and fig. B (which 

 is a horizontal section showing division in the transvei"se direction) 

 that the nuclei may com})letely divide and move some distance 

 apart before constriction of the cytoplasm takes place. From 

 one or two observations made on very young porcellios in process 

 of moulting, I am led to think that the constriction may even be 



