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On the Existence of Cell Communications between Blastomeres. 

 By Ckesswell Shearer, Trinity College, Cambridge. 



(Communicated by Adam Sedgwick, F.K.S. Eeceived January 30, — Read 



February 15, 1906.) 



[Plate 18.] 



Several years ago in following the development of the larval excretory 

 organs of the Serpulid Eupomatus, I had in the course of the investigation to 

 section a large number of the gastrula stages of the egg of this worm. From 

 time to time, in some of these sections I noticed delicate strands of 

 protoplasm traversing the segmentation cavity or portions of this space, 

 connecting one cell with another, or one blastomere with its neighbour. 

 These connections were similar in many respects to the " filose " strands 

 described by Andrews (1), which he has observed joining the blastomeres, in 

 a number of Metazoan eggs during life. I also noticed they were some- 

 times present in advanced stages where their filose character was 

 somewhat different from their appearance at an earlier date. I paid them 

 little attention at first, considering them the result of the action of the 

 fixing reagent in coagulating the albuminous fluid of the blastocoel, or what 

 was still more probable, to the imperfect penetration of the reagent, and 

 the consequent necrosis and disintegration of the protoplasm in the interior 

 of the egg. Meeting with them again and again in the course of the work, 

 and under conditions that seemed to show they were not due to either of 

 these causes, I was led to make a few experiments to determine if possible 

 their nature and significance. 



Their presence, I found, was well marked, in eggs preserved with any 

 of the good fixatives, especially those that act rapidly, such as the Osmic 

 acid mixtures, and Corrosive-acetic. The action of these is sufficiently 

 different to preclude the strands being therefore of the nature of ordinary 

 coagulation artifacts. On the other hand, it was impossible to ascribe 

 them to the breaking up of the protoplasm and imperfect fixation, as 

 in many of the eggs in which they were present all the finer histological 

 details were well preserved, and in some cases the various phases of mitosis 

 plainly shown. 



- Their observation on the living egg I found difficult on account of 

 their transparent nature during this state, and also on account of the 

 difficulty of examining the interior of the segmentation cavity satisfactorily 

 in the whole egg under the high power of the microscope. By placing 



