Introduction to Animal Morphology. 237 



minute, and has been noticed making 45-180 con- 

 tractions in one way, then pausing for a time equal- 

 ling the duration of two beats, and then making 170 

 contractions the other way. The blood is colourless, 

 with ovoid or irregular corpuscles, rarely red. The 

 heart is absent in Pelonaia. In Salpa it sends a branch 

 to the closely united mass of viscera ("nucleus"), and 

 a haemal canal to the branchial chamber. 



There are no external generative organs. Self- 

 impregnation occurs, except in those cases of pro- 

 tandry where the spermatozoa are earlier developed 

 than the ova, or in the dioecious forms. The testes 

 are three or four milk-white pouches, usually around 

 the ovary, and opening on a mammillary eminence into 

 the cloaca. They are rarely symmetrical (Pelonaia). 

 The spermatozoa have discoidal bodies and flagella. 

 The ovary is usually a sac, opening into the cloaca ; 

 single (Phallusia), double (Boltenia, Pelonaia), race- 

 mose ' (Cystingia) opposite to it. Cants describes a 

 second gland secreting the gelatinous covering of the 

 ova. 



The eggs are rarely developed directly, usually 

 with the intervention of a larval stage, and sometimes 

 one or two metagenetic forms intervene between each 

 act of sexual reproduction (Doliolum). 



In Ascidia and Phallusia the segmented yelk as- 

 sumes its mulberry form, hollows within, and appears 

 as a spherical, cellular body (blastula) ; a groove in- 

 dents one side of this ; the lips of the groove rise and 

 close it in, except at one spot, and thus the body be- 

 comes bicavitary, the dorsal groove contracts, and the 

 nerve ganglion develops either within it, or in its close 

 vicinity. On a plane between the dorsal neural cavity 



