92 NOTES AND OBSERVATIONS ON BOARD H.M.S. RATTLESNAKE 



endogenous development occurs, and would seem in some cases to 

 represent sexual propagation. Now the mode of this endogenous 

 multiplication presents remarkable features of similarity in the In- 

 fusoria, the Gregarinidas, and the Sponges. 



There is a certain period in the existence of Vagmicola aystallina, 

 when, gorged with food stored up in the shape of fat granules, &c., 

 within the cavity of its cell-body, it becomes sluggish and eventually 

 still. The body contracts and becomes rounded, and the transparent 

 case closes in and seals up its inhabitant. Eventually long processes 

 are developed from the body, and it takes on the form of the genus 

 Acineta of Ehrenberg. After a while a new life stirs within this 

 chrysalis-like form, and the contained mass gives rise successively (by 

 a sort of fission) to young ciliated bodies, which leave the Acineta and 

 become Vaginicolcc. 



In a similar manner Vorticella inicrostouia becomes Podophrya 

 jixa ; but sometimes the changed Vorticella has no stalk, and then is 

 the Actinophrys of some authors (not A. Sol). It is not known in what 

 way the embryos are brought forth here, but it is a very significant 

 fact that both the stalked and unstalked forms have been observed to 

 conjugate. 



Epistylis presents similar phcTenomena. 



The Actinophrys Sol, to which more particular reference will be 

 made by and by, has been observed to conjugate, but it is not abso- 

 lutely known to arise by the metamorphosis of any Vorticella, though 

 there is every probability in favour of the supposition that it does. 



The Gregarinidje pass through similar changes. Two forms of 

 these creatures are known ; the one consisting of protean nucleated 

 cells, the other of motionless spherical sacs, containing a vast number 

 of minute bodies resembling Naviculce in shape, and thence called 

 " Navicella-sacs.'' Now, according to Stein, although the fact has 

 been doubted by others, the '' Navicella-sacs " result from the conjuga- 

 tion of two GregarincE, which have become motionless and filled with 

 an accumulation of granules. 



Certain it is that the Navicellae are developed within the granular 

 mass like embryo-cells within the yelk, and that when freed by the 

 bursting of the Navicella-sac they become Gregarince. 



Lastly, in the freshwater sponge {Spongilla), which consists of an 

 aggregation of nucleated protean cells like a mass of Gregarince, a 

 certain number of the cells at various points scattered through the 

 substance of the Spongilla become motionless and distended with 

 granules, and receiving first a membranous and then a siliceous in- 

 vestment, constitute the " seed-like bodies.'' 



