56 SUMMARY OF CURRENT RESEARCHES RELATING TO 



highly refractive, the tail very fine and very delicate. This is what 

 is seen in a mature sperm-sac. 



In an immature one we find a very different arrangement : a young 

 sac is small, and has finely granular colourless contents ; the proto- 

 plasm is homogeneous. In other small sacs we may find at the centre 

 of the protoplasm a transparent sphere, which clearly represents a 

 nucleus. In fact, at this stage the contents of a male sac look exactly 

 like those of the female. The sui-face of the protoplasm next becomes 

 covered with bosses formed by grooves ; soon several separate proto- 

 plasmic spheres become apparent, while the central mass is, of course, 

 diminished in size ; the spheres vary greatly in size ; during this pro- 

 cess of segmentation the nucleus remains intact. In other cases the 

 protoplasm of the cell is seen to be broken up by the formation 

 within it of clefts and spaces ; but, as in the other, the result is the 

 disintegration of the primitive mass, the superficial laecoming distinct 

 from the central portion. Yet in other cases, and especially in the 

 autumn, cells in which no nucleus was apparent were observed to 

 develope a stellate space within themselves ; here no central proto- 

 plasmic mass was left. The nucleus, then, does not appear to be 

 essential to spermatogenesis, and it is the peripheral and not the 

 central portion of the cell that becomes converted into spermatozoa. 



If we now fix our attention on the peripheral bodies, we find that 

 in each there arise endogenously a number of large-sized granules, 

 while at the same time the protoplasm of the spherule elongates, be- 

 comes fusiform and transversely striated. The filaments which corre- 

 spond to the striae become more and more independent, the intermediate 

 zone atrophies, and the filaments take on the definite form of the 

 spermatozoa. 



To sum up : The seminal sac of the Nemertinea forms spermatosporesy 

 or male ovules, composed of a mass of finely granular protoplasm, in 

 which a nucleus may or may not be developed. The central portion 

 tends to atrophy, while the peripheral takes on the form of plates or 

 spheres which become attached to the inner wall of the sac. The 

 central portion is the protohlastophor, the peripheral spherules the 

 protospermohlasts. From each of these we get deutohlastopJiors, and 

 deutospermohlasts which become spermatozoa. 



Development of Trematoda,*— H. Schauinsland, after an elaborate 

 account of the views of his predecessors in this field of inquiry, gives the 

 results of his own observations on eight species of Distomum, and on 

 Aspidogaster concjiicola. His general results may be thus summed 

 up : The Trematode ovum is made up of the true egg^cell and of the 

 yolk, which at first arises, more or less, from large, rounded, nucleated 

 cells ; the egg-shell is formed by a highly coloured chitinous mem- 

 brane, in which a long and a transverse axis can be generally detected ; 

 at one end there is nearly always an operculum, and that end is also 

 that of the head. Cleavage is complete though irregular, being of 

 course more or less dependent on the amount of yolk ; the result is a 

 solid mass of cells, which in time absorbs the whole of the yolk ; 



* Jenaisch. Zeitschr. f. Med. u. Naturwiss., xvi. (1883) pp. 464-527 (3 pls.X 



