54 C. 0. AVhitmHn 



sous des angles dièdres ; les germigène a une forme polyédrique.« 

 (1, p. 53.) 



Since the peripheral cells do not — at least in the first instance — 

 arìse endogenously , but by divisiou , their cohesion evidently requires 

 an explauation. 



If the view bere preseuted be the correct one, an interesting 

 question arises, to which I am unable to give any positive answer. 

 Does the first generation of cells produced by the germogen displace 

 the peripheral cells previously formed by division ? In other words, is 

 the peripheral layer of the Infusorigen, in stages later than fig. 110, a 

 product of the germogen? and is this layer replaced as often as a new 

 generation of cells arises within the germogen ? 



The description given by Van Beneden would answer these ques- 

 tions in the affirmative . I bave tried in vain to satisfy myself on this 

 point, but I may remark that such an answer would lead us to suppose 

 that a considerable uumber of lufusorific germ- cells would come to 

 maturity simultaneously. Fig. 111 represents a tyi^ical case, from 

 which I have never seen any very wide departures in y o u u g Infuso- 

 rigens. In this instance, not more than two germ-cells can be Said to 

 have reached muturity at the same time. The fact that the stages of 

 development are more and more advanced as they recede in either 

 direction from the Infusorigen, shows plaiuly that not all of the periph- 

 eral cells can arrive at maturity at the same time. So far as I can 

 learn, the germ-cells leave the Infusorigen at maturity, or shortly be- 

 töre, generally one or two at a time. In size and general appearance 

 the ripe germ-cells agree with the larger cells of the peripheral layer, 

 and I see no reason todoubtthat they arise directly from this layer. 

 If this be the case, this layer is probably replaced gradiially by 

 cells originating in the germogen. The comparison of the Infusorigen 

 in its earlier phases with the developmental stages of the vermiform 

 embryo is not, however, afiected by the answer which may be given to 

 these questions. 



A Review of the Subjeet of Reproduetion. 



The phenomena of reproduction in the Dicyemids are in some re- 

 spects unique, but, for the most part, not without analogies. It is my 

 object to present bere a general survey of these phenomena so far as 

 now known , to interpret them so far as I may be able , and to consider 

 some of their bearings. 



We do not yet know how the Dicyemids pass from one Cephalo- 



