494 TUNICATA. 



the genital organs, lies the egg-cell surrounded by smaller undif- 

 ferentiated cells from which the follicular epithelium is derived. A 

 cell-mass attached to the follicular epithelium and lying proximally 

 to the left of the egg-cell represents the rudiment of the testis (Fig. 

 253, h). In the young rudiment of this organ, a superficial epithelium- 

 like layer of cells can be distinguished from a central mass of cells. 

 The seminal duct forms as an outgrowth of the peripheral epithelial 

 layer. The oviduct ai-ises in a similar way from the egg-follicle, and 

 both ducts open into the atrium. In later stages, the rudiment of 

 the testis becomes lobate. Two eggs occasionally occur in the egg- 

 follicle, one being larger than the other. The smaller egg seems to 

 disintegrate later, so that only one egg is maturated in each indi- 

 vidual in Pyrosoma as in the Salpidae. 



4. Salpidae. 



The processes of budding in the Salpidae early attracted the 

 attention of zoologists and have been repeatedly investigated. 

 Eschricht, Huxley (No. 95), Leuckart (No. 98), and Vogt laid 

 the foundations of our knowledge of this subject, and in more recent 

 times it has been increased through the application of modern methods 

 by Kowalevsky (No. 96), Todaro (No. 107), Salensky (Nos. 101 

 and 102), Seeliger (No. 105) and Brooks (Nos. 92 and I.). No 

 very satisfactory comprehension of the ontogenetic processes has, 

 however, as yet been attained. Brooks was able to trace back the 

 budding of the Salpidae to the type observed in Pyrosoma, point- 

 ing out that the biserial arrangement of the buds on the stolon of the 

 former is the result of lateral shifting and the simultaneous rotation 

 of the buds round their longitudinal axis. Since this latter point was 

 overlooked by the other authors, we must regard with some doubt 

 their statements as to the rise of the organs in the buds. 



In SiiIjik, the buds arise on a proliferating stolon (Fig. 262, st) 

 which must be regarded as in every way homologous with that of 

 Pyrosoma. In older embryos (Figs. 216, st, 224 B, s) this can be 

 seen as a conical outgrowth at the posterior end of the endostyle 

 growing out between it and the opening of the oesophagus rather to 

 the left side of the body. When the stolon grows longer, it appears 

 embedded in the cellulose mantle of the solitary individual. A cavity 

 containing the stolon develops, however, in the mantle-substance 

 (Fig. 262, h) and this finally opens externally (o), so that the distal 

 end of the stolon from which the mature buds are abstricted, projects 

 out freely. The position of the stolon differs in the various species. 



