844 



TESTIS. 



encysted stage, in the ox ; Tnia coenurus, in the dog's intestine ; the encysted stage, or 

 Coenurus cerebrnlis, in the brain of the sheep, where it gives rise to the condition of 

 44 staggers "; Tsenia echinococcus, in the dog's intestine ; the embryos or scolices occur in the 

 liverof man as " hydatids. " t 



The meduste also exhibit alternation of generations, and so do some insects, especially the 

 plant liee or aphides. 



TO. Parthenogenesis (Owen, v. Siebold). In this variety, in addition to sexual reproduction, 

 new individuals may be produced without sexual union. The non-sexually produced brood is 

 always of one sex, as in the bees. A bee- 

 hive contains a queen, the workers, and the 

 drones or males. During the nuptial flight, 

 the queen is impregnated by the males, and 

 the seminal fluid is stored up in the re- 

 ceptaculum seminis of the queen, and it 



Fig. 628. Fig. 629. Fig. 630. 



Fig. 628. Cysticerci from Tamia solium removed from their capsule. 1, natural size ; 2, 

 magnified. a, embryo-sac ; b, cavity produced by budding of the embryo-sac ; c, 

 suctorial discs and hooklets. Fig. 629. Cysticercus of Taenia solium, with its head and 

 segments protruded, a, caudal-sac ; b, head of the tape-worm, with discs and booklets 

 (scolex) ; c, neck. Fig. 630. Part of an Echinococcus capsule, with developing buds. 

 a, sheath ; b, parenchymatous layer ; c, germinating capsule filled with scolices. 



appears that the queen may voluntarily permit the contact of this fluid with the ova or with- 



h old it. All fertilised eggs give rise to female, and all unfertilised ones to male bees. 



Vlll. Sexual reproduction without any intermediate stages occurs in, besides man, mammals, 



birds, reptiles, and most fishes. 



432. TE8TIS SEMINAL FLUID. [Testis. In the testis or male reproductive organ, 

 the seminal fluid which contains the male element or spermatozoa is formed. The framework 

 of the gland consists of a thick strong white fibrous covering, the tunica albuginea, composed 

 chiefly of white interlacing fibrous tissue. Externally, this layer is covered by the visceral 



^omari 



1ffI,ran ^^ imnjOTu^^ 



Fig. 631. Taenia mediocanellata. Natural size. 

 layer of the serous membrane, or the tunica vaginalis, which invests the testis aud epididymis. 

 The tunica albuginea is prolonged for some distance as a vertical septum into the posterior 

 part of the testis, to form the mediastinum testis or corpus Highmori. Septa or trabecular 

 more or less complete stretch from the under surface of the T. albuginea towards the medias- 

 tinum, so that the organ is subdivided thereby into a number of compartments or lobules, 

 with their bases directed outwards and their apices towards the mediastinum. From these, 

 finer sustentacular fibres pass into the compartments to support the structures lying in these 

 compartments.] 



