Xo. 4. — Crififatdla: the Orujiii and Jkvclopmnif of Ihr 

 valued in, the Colony. By C. 15. ])AVENi'Oia'.' 



In,!i- 



Contents. 



Page 



I. Tntroduction 101 



II. Ar(-liiti.'cture of tlie C(jl()ny . lUo 

 III. Ori-in of tlic Inilivi.luul . . lOG 



A. (Jb.servatioiis. — Origin of 



1. Tlie Uud .... 107 



2. The Alimentary Tract 111 



3. The Central Nervous 



System 11-) 



4. Tiie Kamptoilerm . 115 



5. The Fimienhis ami 



jMuscles . . . . ll'i 



6. Tlie IJotlywall . .117 



7. The Radial i'artitions llO 



B. Comparative ami Theo- 



retical IJevicw of the 

 Observations on the 

 Origin of the Indi- 

 vidual 120 



Origin of the Poiypide 121 

 Interrehition of the 

 Individuals in tiic 



Colony 121 



Origin of tiie Layers 123 

 Origin of tiie Alimen- 

 tary Tract . . . .127 



1. 



2. 



3. 



4. 



I';i<:.. 



5. Origin of the Central 



Xervous System . 1"_'7 



G. Origin of the runicu- 



his ami Muscles . li'^ 

 IV. Organogen\'. — Development of 



1. The Ring Canal . . 12'.i 



2. The Lophophore . . IH" 



3. Tiie Tentacles . . I'i-'i 



4. The i>oi)hophoric 



Nerves 13(! 



T). The Kjjistome . . . 13S 

 (]. The Alimentary Tract l;!'.t 



7. The Funiculus .and 



Muscles . . . . Ul 



8. Origin and Develop- 



ment of the I'arieto- 

 vaginal Muscles . .14:! 



9. Disintegration of the 



Neck of the Poiyp- 

 ide 144 



10. Development of the 



Body-wall .... 144 



Summary 14f) 



Bibliography 148 



K.xplanation of Figures .... 152 



I. Introduction, 



At the suggestion of Dr. 1-",. I,. Maik, I liogiui, in tlie sjn-ing of 

 1889, the stiiily of iVesli-watcr Ilnozoa. While :it the [.ahoi-aturv of the 

 riiite(l States Fish ( 'liimnissidii, at Woods Holl, iMass., where, tlirougl. 

 tlic kindness of ]Mr. A. Agassiz, 1 h;i(I the opjiort unity of speiidiii^' tl: 



• Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology, under the direction of Iv L. Mark, No. XI.X. 

 VOL. .\.\. — NO. 4. 



