Papers from the Marine Biological Laboratory at Tortugas. 205 



the words "apyrene" and " oligopyrene " are sufficiently descriptive to 

 distinguish them from the true or "eupyrene" spermatozoa. Then again, 

 they are spermatozoa in the sense that they are products of the testis and 

 are found in the seminal fluid along with the true spermatozoa. 



In retaining these names the writer does not mean to imply any homology 

 between the apyrene and the eupyrene spermatozoa. Indeed, on account 

 of the absolute lack of homology the terms "apyrene spermatocyte" and 

 "apyrene spermatid" must be abandoned. A spermatocyte is a cell which 

 is derived directly, by a mere process of growth, from a spermatogonium, 

 and a spermatid is one of the four cells resulting from the two maturation 

 divisions which such a spermatocyte has undergone and which is then 

 transformed into a spermatozoon. The cells which give rise to the apyrene 

 spermatozoa of Stromhiis go through two distinct periods of development and 

 at no time can they be homologized with either the eupyrene spermatocytes 

 or spermatids. 



The first of these periods starts at the time when the cell is first recog- 

 nizable in the testis.^ This period continues throughout all the stages of 

 the gradual but great growth of the cell and ends with the breaking down 

 of the nucleus and the simultaneous scattering of the centrioles. The 

 second period may be said to begin with the division of the centrioles; it is 

 a period of marked cytoplasmic differentiations and it ends, of course, with 

 the formation of the fully matured apyrene spermatozoon. For the cell 

 during the first period it is proposed to use the name "apyrene spermato- 

 blast" and during the second period to designate it as the "apyrene sper- 

 matosome." Both of these words, "spermatoblast" and "spermatosome," 

 have been used hitherto in various connections; neither of them has the 

 restricted meaning of "spermatogonium" or "spermatocyte" and, as used 

 here, they imply no homologies with either of those structures. 



METHODS. 



Several fixatives were used for preserving the testis and the uterus of 

 Stromhiis, namely, Bouin's, Flemming's, Helly's, and Zenker's fluids. Of 

 these, Flemming's fluid (strong solution) gave by far the best results. Small 

 pieces of the tissue were fixed for from 6 to 8 hours and were then washed 

 for at least the same length of time, usually over night. As a result of such 

 fixation the osmic and acetic acids did not penetrate very strongly into the 

 inner portions of the tissue, and here the preservation of the mitochondria, 

 the spheres, and the fibers was all that could be desired. 



Sections were cut 5 micra thick and were stained with iron haematoxylin, 

 followed by a weak solution of erythrosin in 70 per cent alcohol, which had ' 



1 It may be well to state at this point that the writer has succeeded in tracing the origin of these back to 

 the so-called basal nuclei of Platner. He has found that the nurse-cells in the testis of Littorina have a similar 

 origin, although the developmental changes are less complicated. It was deemed best, however, not to present 

 the evidence of this origin at this time, but to wait until the history of the basal nuclei had been followed, in all 

 its details, not only in these forms but also in other Prosobranchs, both those which have dimorphic spermatozoa 

 and those which do not. The scope of the present paper, therefore, is confined to a description of the develop- 

 ment of these cells from the time when their nuclei have been completely differentiated from the basal nuclei 

 and have been established in the syncytium of the testis along with the true spermatogonia, each one surrounded 

 by its own definite cytoplasmic body. 



