ECONOMY OF THE ACEPHALOCYSTS OF AUTHORS. 5(55 



are separated by a constriction, across which a diaphragm stretches (PI. XVI., fig. 

 13, C), formed of two layers, of very fine cellular substance, derived from, or con- 

 tinuous with, the cellular substance, and forming the walls of the head and pedicle. 

 This cellular substance is confined between two layers of membrane, namely, 

 that already described as derived from the external membrane of the vesicle, and 

 another which forms the internal cavitary surface of the pedicle. (PL XVI., fig. 13, 



F-) 



The head is armed superiorly with a double circle of long bent teeth (PL XVI., 

 fig. 12, A), which are barbed on one edge, and arise from one common disk. 

 Around this dotible coronet of teeth, and on the sides of the head, are four trans- 

 versely oval suckers, which are surrounded by two concentric bands. (PL XVI., 

 fig. 12, B.) 



The pedicle to which this head is attached contains layers of gemmules, by 

 which this animal propagates. (PL XVI., fig. 13, G H.) I have been unable to de- 

 tect any organ by which these gemmules pass off from the pedicle to the place 

 where they are developed, i. <?., between the layers of the cyst of the parent. 



In many cases which have come under my observation, young heads have 

 been observed sprouting from the side of the parent pedicle. In this case, how- 

 ever, the cells from which these young heads derived their origin were precocious ; 

 for in general the young cell never put on an active character till it reached 

 a proper nidus between the layers of the parent vesicle, which was generally near 

 the base of the parent pedicle, but sometimes the nidus was at a greater distance. 

 These circumstances would lead us strongly to suspect that there is no efferent 

 vessels for conveying the young gemmules out of the pedicle. (PL XVI., fig. 1.) 



The gemmule, in its earliest stage, consists of a germinal vesicle (C), containing 

 a germinal spot (D), a yelk with its proper membrane (B), and a thin layer of 

 albumen, enclosed in a strong covering or shell (A.)* After it has escaped from 

 the parent, that is, after it has left the pedicle, the development commences. 



During the second stage, the nucleus has increased very much in size (D). 



During the third stage the nucleus has become nodulated (PL XVI., fig. 3, D), 

 much larger, and a clear central space, which was observed before, has also in- 

 creased in size. 



During the fourth stage the nodules of the nucleus have assumed the form 

 of cells, and have become arranged in a circle round a central cell. (PL XVI., 

 fig. 4, E.) 



During the fifth stage the young cells have gradually increased in size, and 

 have filled the germinal vesicle (PL XVI., fig. 5, CD); the central cell has also 

 become larger, and its nucleus has acquired a clear central spot. (PL XVI., fig. 5, 

 FG.) 



* These different parts of the ovule are probably only analogous to those of the higher animals. 

 VOL. XV. PART IV. 7 O 



