708 William Patten 



in the retina oiPecten produce very fine lateral branches, which become 

 attached to neighboring sense cells. The same process takes place upou 

 the epidermis, so that one of the slender sense cells (PI. 32, fìg. 153, d], 

 which stili retains its sense hairs, becomes unìted to a neighboring 

 sense celi [e] by fine fibres. The advantage thiis gained is too great to 

 be left undeveloped, therefore the celi (/) assumes more and more the 

 sensitive roll, while [f^ — ^j gradually losing its sense hairs, and there- 

 fore the power of receiving direct Stimuli, only transmits the Stimuli re- 

 ceived from (/j . We bave uow reached the last change in the develop- 

 ment of these cells; ali are reduced to the same level, since each is 

 subservient to a single function. The most highly developed sensory, 

 nervous, and coutractile Systems are only modifications of the condition 

 represented by these three cells. The celi (/) is the sense organ [sy, the 

 muscular system, and {ß — ^j \\^q nervous centre, which is connected on 

 the one band with the receptive centre for energy, or the sense organs, 

 and on the other, with the contractile centre, or organs of motìon. The 

 specialization , or growth of ali three Systems must go band in band ; 

 increase of one is life to the other, the loss of one, death to the other. 



Sensory, muscular, and nervous Systems must primarily bave 

 originated from the same areas, and the growth of one in a given di- 

 rection is followed by that of the other. 



As the origin of purely sensitive, and of conducting cells, took 

 place after the origin of purely contractile ones , so we find, even in 

 highly developed forms, a more intimate connection maintained between 

 sense organs and nervous centres, than between the contractile centre 

 and either of the other two. The above described diflferentiation gave 

 rise to four sets of cells, which may be divided into two similar groups: 

 Al, the hylophagous cells, situated at the vegetative pole of a spherical, 

 or ovoid, multicellular animai; A'^, contractile cells forming a ring 

 around the vegetable pole ; and a third ring, outside of, and concentrie 

 with the other two, consisting of (Ri) sense, and (B^) nervous cells. The 

 remaining part of the body would be composed of nearly indifferent 

 cells. 



The continuai transformation of sense cells into conducting, or 

 gauglionic ones, with deeply situated nuclei, gave rise to a ring of 

 ganglionic cells whose union with each other and with the contractile 

 cells became more and more complicated. 



A sense organ is a collection of cells for the reception 



1 Unfortunately, not represented in the figure. 



