216 



THE ACEPHALA. 



^ 198. 



that of the parent, and the envelope of the mantle alone is common to 

 both/') 



§ 198. 



With the Acephala, the sexes are sometimes separate, sometimes united 

 in one individual. But the genital organs are very fully developed, and, 

 as with the Zoophytes, consist of an ovary and a testicle with an excretory 

 duct ; but in none are there copulatory organs, or uterine reservoirs for the 

 eggs. 



The eggs are usually spherical, rarely pyriform or elliptical. The pale 

 yellow or reddish vitellus is finely granular, and surrounded with a vitel- 

 line membrane and a smooth colorless chorion. 



The germiuative vesicle has usually two nucleoli cemented together. 

 Often there is a layer of white substance interposed between the chorion 

 and the vitelline membrane. ''> 



The sperm is milky, and, at the epoch of procreation, quite full of very 

 active spermatic particles. These always consist of an oblong, oval, or 

 pyriform body, to which is abruptly attached a delicate tail, whose motions 

 are not aifected by the water in which these animals live.^"' 



With the Acephala of separate sexes, the ovaries and testicles so closely 

 resemble each other, not only as to their form and the arrangement of 

 excretory ducts, but also as to their locality in the body, that they are 

 with difficulty distinguished each from the other, except at the period of 

 procreation. 



The copulatory organs being absent, here, as with the Zoophytes, the 

 water is the fecundating medium. 



1 This multiplication by buds has been observed 

 by Milne Edwards with Botri/llus, Polyclinum, 

 Amaroucium, Didenuium, and Perophora. It 

 occurs also, undoubtedly, with other compound 

 Ascidiae, and is the cause of the increase of the 

 Ascidian-stock with the colonies of these animals. 

 With the simple Ascidiae — Clavelina lepadifor- 

 mis, and prodii.cta, the buds take the form of 

 suckers (Stolones), and the new individuals are 

 separated from their parents with the separation of 

 the mantle ; see Milne Edwards, Sur les Ascidies 

 compostes, loc. cit. p. 41, PI. III. lig. 2'. {Ama- 

 roucium proli/erum), PI. VII. 1, 1''. 1«. {Bo- 

 try lloides rot if era), and PI. II. fig. 1«. 3 {Clav- 

 elina), Eysenhardt (Nov. Act. Acad. Leop. Carol. 

 XI. p. 263, Tab. XXXVI. fig. 1, &c.), has also ob- 

 served these stolons upon a simple Ascidian. 



1 These eggs have been figured by Warner, Pro- 

 dromos, &c., p. 7, Tab. I. fig, 5 ; Cams, Erlauter- 

 ungstafeln, &c., lift. V. Xaf. 1, fig. 2, and Nov. Act. 

 Acad. Leop. Carol, loc. cit. p. 26, Tab. I. {Ano- 

 donta and Unio), and by Milne Edwards, Sur les 

 Asoid. comp. p. 25, Pi. IV. fig. 1-3 {Amaroucium). 



2 The spermatic particles of the Acephala have 

 been descril)ed and figured by IVai;ner, in Wiei;- 

 mann's Arch. 1835, II. p. 218, Taf.IlI. fig. S 

 (Cyclas); Siebold, in Mailer's Arch. 183T, p. 

 381, Taf. XX. fig. 12-14 {Unio, Anodonta, My- 

 ti/us, Tichogonia, Cardium, Tellina, Mya and 

 Cyclas); AT oWiXer, Beiti'age, loc. cit. p. 37 {Pho- 

 las), and Krohn, in Fruriep's neue Not. No. 356, 

 p. 49, 52 {Phallusia and Salpa). Those of Ama- 

 roucium described by Milne Edwards (loc. cit. p. 

 21, PI. III. fig. 1<^.) differ from the usual type in 

 being fusiform and very long, — their tail not being 

 distinct from the body. Those of a Cynthia have 

 appeared to me of a similar form, — only the tail 

 was much longer and more delicate. With Phal- 

 lusia, on the contrary, I have distinctly seen them 

 with an oblong body to which is abruptly attached 

 the tail. The sperm of Polyclinum, Botryllus, 

 Didemnum, Diazona, and Phallusia, contains 

 spermatic particles of a Cerciiria-form ; while those 

 of Salpa are filamentoid ; see Kslliker, Neue 

 schweiz. Denksclu-. VIII. p. 43, fig. 30, 49, 53-67.* 



* [ § 198, note 2.] The spermatic particles of 

 the Acephala throughout, are according to my own 

 observation, of a Cercaria-like form, — that is, hav- 

 ing a distinct head to which is attached a more or 

 less delicate tail. Their development, which I 

 ^ave traced in many cases, is in special, daughter- 

 cells as with all other .animals. They may, as 

 indeed they often do, assume various groupings 

 afterwards, but the real development appears sim- 

 ple and invariable. The rfiape of the head of the 



particle I have found to differ widely, yet in each 

 case to present an uniformity of a zoological value. 

 Sometimes it is perfectly globular {Polyclinum\ 

 sometimes oval {Unio, Anodonta), sometimes ova- 

 globular {Ostrea), sometiiaes oblong {Ascidiay, 

 sometimes pyriform {Mytilus}, sometimes conico- 

 pyriform {Mya}, and sometimes long-conical {Cy- 

 prina). These forms may seem a refinement more- 

 ideal than real, but the exact forms are determincij 

 by micrometi'ical measui'ements. — Ed. 



