34 G. H. Park 



arker 



This organic independence in Stylotella also appears in the 

 almost complete absence of transmission from part to part. The 

 opening and closing of an osculum on one finger in accordance 

 with the condition of the surrounding water has no influence on 

 adjacent oscula even though they be only a centimeter or so dis- 

 tant. Extensive wounds, which can be made with much local 

 precision, influence oscula or ostia only within a very close range. 

 Transmission at best cannot be over a much greater distance than 

 a centimeter or so. Nor is the nature of this transmission at all 

 nerve-like. A cut made about 3 mm. from an osculum was fol- 

 lowed by the closure of the osculum only after eleven minutes, 

 though this osculum had previously closed in quiet water in from 

 four to five minutes. The form of reaction resembles that seen in 

 the vertebrate iris, in which in response to a point of light the iris 

 contracts locally, the contraction gradually spreading through 

 the whole organ ( Hertel, '07). In the sponge, as in the iris^ we 

 are probably dealing with the direct stimulation of smooth muscle, 

 which when locally contracted stimulates by its contraction the 

 adjoining resting muscle and thus a slow form of transmission is 

 accomplished through the muscle substance itself. 



These studies of the reactions of Stvlotella support the conclu- 

 sion arrived at from earlier anatomical investigations to the eff^ect 

 that sponges possess nothing that may with propriety be called 

 nervous tissue. Their reactions, which have the general charac- 

 ter of great simplicity and independence, are, I believe, entirely 

 due to the direct stimulation of choanocytes or myocytes which are 

 either on exposed surfaces or close to them and which, at least 

 in the case of myocytes, exhibit a form of progressive stimulation 

 that resembles sluggish transmission. Sponges are metazoans 

 possessing muscular but not nervous tissue. 



5. ORIGIN OF THE NERVOUS SYSTEM 



In seeking evidence on the origin of the nervous system, investi- 

 gators have naturally turned to primitive metazoans, and the 

 coelenterates have afi^orded the principal material for speculation 

 on this subject. These speculations took their origin in the dis- 



