232 HOMOLOGICAL RELATIONS OF THE 



mitted in the case of the spennatic particles, the only 

 instance in which they are walled cells being that of the 

 pollen grains of plants, the real value of which cannot be 

 positively determined till we have greater certitude as to 

 the behaviour of the extremity of the pollen-tube within 

 the ovule. But the female germ is generally regarded as a 

 true walled cell, and is considered moreover to be identical 

 with the primordial cell of the future embryo, passing into 

 it, when fertilized by some material or influence derived 

 from the spermatic particles. 



Yet the grounds are very slender for either of these assump- 

 tions — that is, either for admitting that the female corpuscule 

 is — any more than the male — essentially a true walled cell, 

 or that one of these corpuscules is more continuous than the 

 other with the resulting embryo. The real state of the case 

 appears to be tha;t the embryo is formed out of the combina- 

 tion of masses of protoplasm representing the two sexes, and 

 that it assumes afterwards the form of a true cell by its own 

 progress of groTii;h, the first steps of organization being — at 

 least in animals — what is termed segmentation, and the 

 formation of a wall round the exterior of the mass. 



While it is true that these acts commonly take place within 

 the cell-wall which originally surrounded the unimpregnated 

 germ, this is not to be considered as an essential of their 

 performance, but as due to the accidental circumstance that 

 the commixture of the particles generally takes place by the 

 spermatic corpuscules gaining access to the interior of this 

 protecting cell, through a perforation in its wall ; for when 

 the commixture is effected otherwise the result is different. 

 Thus, while in some of the conjugating Algee the proto- 

 plasmic contents of one cell are transferred to another, with 

 the contents of which they combine and form a spore to be 

 matured in that same cell, in other species of the family 

 Iwth cells effuse their protoplasmic contents, and the spore 

 resultino; from their combination is either matured in a new 



