Exndence from Metazoan Germ-Cells 9 



the body (c. v., figure 36) being all that is left of tlie substance 

 at the late stage represented. So uuieh by way of ilhistratiou of 

 the portions of the s])ermatid, or germ of the sjKrniato/oon. in 

 the vertebrated animals, for des])ite the great variety in struct- 

 ural details presented by the s))('rm of this part of the animal 

 kingdom I think all will agree that so far as concerns the chief 

 ))oint being made in this discussion, what we have ))r('sont<'d is 

 true of the whole ])hylum. 



(b) Illustrated by the Ontogeny of an Insect Sperm 



We will now examine the ontogeny of a very different 

 type of speiTn, from another portion of the animal kingdom, 

 the insecta. The particular species chosen is the fowl-tick 

 {Argas miniatus). The investigation made use of is by 

 Doctor D. B. Casteel. 



The series of figures (42 a, h, c, d, e, f, g,) will help to 

 an understanding of the remarkable, almost unique sperm and 

 spermogenesis in this animal. Figure 42rt shows the nearly ma- 

 ture primary spermatocyte. Especially to be noted are the 

 mitochondria, mi., scattered uniformly through the cytoplasm, 

 and the striated layer, *. /., on the outer surface of the cell. 

 This layer is sharply demarked from the underlying cyto})lasui. 

 The striae, disposed perpendicular to the surface of the cell, are 

 excessively fine, and when looked at in situ end on "suggest the 

 appearance of a faceted compound eye or of honey-comb." ® 

 Concerning the genesis of this layer Casteel says, in a personal 

 letter, that the layer begins to appear at the surface and grad- 

 ually increases in depth until the completed state shown in figure 

 42a is reached. "The striae," he says, "appear to be forming 

 from the undifferentiated cytoplasm sheath." 



All the figures from 42 b to g have to do with the transforma- 

 tion of the spermatid (figure 42b) into tiie spermatozoon, h'rom 

 figure 42b one sees that the striated layer has disap})eared on one 

 side of the cell and thinned out greatly in a smaller area on the 

 opposite side; that the nucleus, n, has moved to the surface of 

 the cell in the middle of the arr-a of disajipearance of the striated 

 layer; that the large plasmosomes, pi. 42a have almost entirely 

 disappeared from the nucleus; that the vesicular bodies r.h., as- 

 sembled for the most part in the vicinity of the nucleus, are 



