INTRODUCTION. XI 



freshwater Polyzoa), amongst the Edoprocta, and in the 

 group of the 'Entoprocta. As this work does not include 

 the PMjlactoIeemata, I shall confine myself at present to 

 an account of the endocyst as it exists amongst the other 

 sections of the class. 



First, then, in the marine Edoprocta the endocyst 

 appears in the adult cell as a delicate transparent mem- 

 brane, without any cellular structure, a layer of simple 

 protoplasm, lining the ectocyst throughout, and generally 

 lying close upon its inner surface^. But though it occurs 

 in this condition in the older regions of the coenoecium, it 

 is essentially a cellular membrane; and its true nature 

 may be readily determined by the study of the growing 

 extremities of a branch or stolon amongst the Ctenosto- 

 mata (for instance), which offer the greatest facilities for 

 investigations of this kind. Here, according to Joliet, 

 the endocyst appears as a very thick layer, and exhibits a 

 distinctly cellular structure. He describes it as composed 



* I may say here once for all that I do not pi-opose to enter into minute 

 histological detail. The space at my command would not allow of my 

 doing so ; and, apart from this, such detail would be out of place in a 

 general sketch lite the present. 



On the structure of the endocyst the reader may consult : — Smitt, " Ora 

 Hafshryozoernas Ut^eckling och Fettkroppar,"CEfv. Kongl. Vet.-Akad. Forh. 

 1865, no. 1, p. 16; Clapaeede, Zeitschr. f. wiss. Zool. xxi. p. 142; Nitsciie, 

 "Ueb. Flusfra memhranacea" Zeitschr. f. wiss. Zool. xxi. Heft 4, pp. 44- 

 46 ; Eeiciiert, " Vergleich. anatomische Untersuchungen lib. Zoohofrt/on 

 •pelluddus (Ehrenb.)," Abhandl. konigl. Ak. d. Wissensch. zu Berlin, 186t>, 

 p. 270 ; JoLiET, ' Bryoz. d. cotes de France,' pp. 56-58, and p. 65 ; Ehi.ers, 

 " Hypoj^horcUa expansa, ein Beitrag zur Kenntniss der minirenden Bryo- 

 zoen," Abhandl. konigl. Gesellschaft d. Wissenschaften zu Gottingen, xxi. 

 1876, p. 27 (sep.). In the Enfoprocfa specially : — Nitsche, " Ueb. die 

 Anatomic von Pedicelli7ia echinafa^' Zeitschr. f. wiss. Zool. xx. Heft 1, 

 p. 18 ; SALEN.SKY, '• Etudes sur les Bryoz. Entoproctes," Ann. Sc. Nat. ser. 6, 

 Zool. vol. V. art. no. 3; Joliet, op. cit. p. 61. In the PhylactoJamafa: — 

 Allman, 'Freshwater Polyzoa,' p. 11; Hyatt, " Observations on Polyzoa, 

 suborder Phylactola'mata," Proc. Essex Inst. vols. iv. & v. 1866-68, p. 26; 

 JOLIET, op. cit. p. .')9. 



