MATURATION OF GAMETES 147 



to the behavior of the cytoplasms of the two developing gametes, it is inter- 

 esting to observe that the idiosome-Golgi-mitochondrial complex behaves very 

 differently in the two gametes (fig. 68). 



A third condition of egg and sperm differentiation involves the possible 

 function of the "nurse cells." In the vertebrate ovary the follicle cells which 

 surround the egg have much to do with the conditions necessary for the dif- 

 ferentiation of the oocyte. The latter cannot carry the processes of differ- 

 entiation to completion without contact with the surrounding follicle cells. 

 Spermiogenesis also depends upon the presence of a nurse cell. In the verte- 

 brate seminiferous tubule, the Sertoli cell is intimately concerned with the 

 transformation of the spermatid into the morphologically adult sperm, and 

 a close contact exists between the developing sperm element and the Sertoli 

 cell during this period (figs. 65, 66, 73). In the discharge of the formed 

 sperm elements into the lumen of the tubule, the Sertoli cell also is concerned 

 (Chap. 1). 



b. Morphogenesis (Spermiogenesis; Sperrnioteleosis) of the Sperm 



1) Types of Sperm. There are two main types of sperm to be found in 

 animals, namely, flagellate and non-flagellate sperm (figs. 74, 75). Flagellate 

 sperm possess a flagellum or tail-like organelle; non-flagellate sperm lack this 

 structure. The flagellate type of sperm is found quite universally among ani- 

 mals; non-flagellate sperm occur in certain invertebrate groups, particularly 

 in the nematode worms, such as Ascaris, and in various Crustacea, notably the 

 lobster, crab, etc. (fig. 75). Flagellate sperm may be either uniflagellate or 

 biflagellate. Single flagellate sperm occur in the majority of animals, while 

 a biflagellate form is found in the platode, Procerodes. However, biflagellate 

 sperm may be found as abnormal specimens among animals normally pro- 

 ducing uniflagellate sperm. 



Conjugate sperm are produced in certain animal species. For example, 

 two sperm heads adhere closely together in the opossum (fig. 125), also in 

 the beetle, Dytiscus, and in the gastropod, Turritella. Many sperm heads be- 

 come intimately associated in the grasshopper to form the so-called "sperm 

 boat" (fig. 76). However, all conjugate sperm normally separate from each 

 other in the female genital tract. 



2) Structure of a Flagellate Sperm. The flagellate sperm from different 

 species of animals vary considerably in size, shape, and morphological de- 

 tails. Some possess long, spear-shaped heads, some have heads resembling 

 a hatchet, in others the head appears more or less cigar-shaped, while still 

 others possess a head which resembles a spatula (fig. 74). The spatula-shaped 

 head is found in the sperm of the bull, opossum, man, etc. The description 

 given below refers particularly to the spatula-shaped variety. Although all 

 flagellate sperm resemble one another, diversity in various details is the rule, 



